Speaking of Confederate generals, let’s analyze the big three Confederate generals:
Longstreet was probably the number one Corps commander of the war. He was a world-class tactician and orchestrated several of the greatest sweeping movements in the American Civil War: sweeping John Pope's flank in Second Bull Run/Manassas, attacking with 20,000 men against an enemy that eventually totaled 50,000 men and still inflicting heavier losses onto his foe on the 2nd day of Gettysburg, smashing the Army of the Cumberland with an impressive, wheeling, columar assault (though his performance was not entirely flawless, see Horseshoe Ridge), and routing Hancock's II Corps in the Wilderness.
However, these great performances should not cover up some of Longstreet's lower moments: his time as independent commander was not anything stellar, the Suffolk Campaign was nothing serious, but his performance in the Knoxville campaign was not good at all. The strategies he proposed were a bit questionable: the famous idea of go between the Army of the Potomac and Washington was unfeasible due to logistical and operational realities, his idea to James Seddon to execute a turning movement after Chickamauga once again ignored logistical realities (see the pattern here?). I think Longstreet's reputation is a bit overblown here and there, but he deserves the title of 'Greatest Tactician' and not...
Jackson: Jackson's reputation as a master tactician and strategist is rather baseless. After from his lackluster performance in the Seven Days Campaign, Jackson opened the Second Manassas Campaign by nearly getting whipped by Nathaniel Banks' numerically inferior force at Cedar Mountain, and was saved by A.P. Hill's arrival and Jubal Early's actions. At Brawner's Farm, he somehow failed to destroy a still green Iron Brigade under John Gibbon, 2,100 man strong, and Doubleday's eventual 800 man reinforcements with 5,900 veterans and the element of surprised. The battle was micromanaged by Jackson, and he did so poorly, sending in units piecemeal. He did decently at parrying Pope's poorly organized thrusts, but when Longstreet pitched his corps into the fray, Jackson sat there with an entirely fresh reserve division, allowing John Pope to shift units to fight a rearguard action against Longstreet.
In the Maryland Campaign, Jackson performs well enough, though I must note that Harper's Ferry was an easy win thanks to a foolish decision not to evacuate and Jackson's lines were saved by a lack of coordination by Union commanders in Antietam. At Fredericksburg, Jackson allowed a severe gap in his line, allowing Meade's division to breach his line, resulting in a fluid, close combat, and costly fight for both sides. Had Reynolds' entire Corps been pitched in, Jackson may have well been defeated.
I have no real criticism of his performance at Chancellorsville, but his flanking march has been overhyped. Total secrecy was not maintained, Sickles' men discovered the march but Hooker deluded himself into believing it was a retreat. The flank attack routed the XI Corps (which put up a better fight than history remembers), but that's not surprising when Jackson had 30,000 men against Howard's unprepared 12,000. The flank attack ultimately sputtered out against Alpheus Williams' division of the XII Corps, and Jackson and Lee were still separated.
Where Jackson deserves credit is Operations and Grand Tactics: in the Valley Campaign, Jackson's operations were excellent, successfully panicking and distracting Washington, while taking advantage of the divided Union commands in the Valley. In the Second Bull Run campaign, Jackson's bold and well-executed maneuver to Pope's rear was what allowed for Lee's greatest victory. Very rarely did independent forces work smoothly in conjunction towards a single goal; Jackson, when detached from Lee in the Valley and Second Bull Run, perfectly understood his commander's intent and was able to accomplish his mission. That's a credit to him. Speaking of plans, the man who composed Jackson's mission for the Valley and Second Bull Run Campaign was...
Lee: Though the Lost Cause tends to hype up Lee's abilities to stratospheric levels, it must be said that Lee was the best Confederate general. After his messy start at West Virginia and the Seven Days Campaign due to poor execution, overambitious plans and shoddy staff work, Lee finally molded the Army of Northern Virginia into an aggressive fighting force, much like how Grant transformed the Army of the Tennessee (and later the Army of the Potomac) into a well-oiled fighting machine. Lee's qualities were his canny use of his subordinates, a good read of his opponents, and a willingness to seize an opportunity presented to him. The Second Manassas Campaign is a good example of where Lee's qualities as a general truly shines.
Contrary to popular belief, Lee was not a terrible strategist on a campaign level. While serving as Davis' military advisor, Lee actually devises the only plan the Confederates implement in Virginia that represented a reasonable use of the operational art with his usage of Stonewall Jackson's Valley Campaign to keep Union reinforcements from reaching McClellan near Richmond. Jackson of course, plays his part in Lee's vision perfectly here. Then, Lee further displays sound judgement at the end of the Valley Campaign; when Jackson wants to continue north and continue threatening Washington, as appealing as this might have sounded, Lee correctly judges that Jackson's diversion has served its purpose and brings his troops to Richmond in time to achieve near-parity with McClellan's forces for the Seven Days Campaign. The resulting campaign was not coordinated very well, but Lee's strategy plays out and McClellan is neutralized for the time being. Lee plans well and across a broad area, incorporating multiple forces, and seizes the initiative and does not relinquish it. On the minus side, new to his army (like Grant with the Army of the Potomac in 1864), his forces don't coordinate terribly well during the Seven Days, and somewhat by accident, he ends up launching costly frontal assaults at Malvern Hill.
The Second Manassas Campaign is in many ways Lee's crowning achievement strategically. Faced with the dual threat of McClellan still on the James and John Pope's advance in Northern Virginia, Lee carefully manages his forces, detaching enough troops to blunt Pope's advance. When McClellan shows signs of withdrawing, Lee acts immediately and decisively, racing north with most of his army to confront Pope. Pope conducts a competent withdrawal behind and defense of the Rappahannock line, preventing any major clash initially, so Lee takes a risk to seize the initiative again, detaching Jackson to strike into the rear of Pope's army at his supply lines, and causing Pope to lose control of the campaign. Lee and Longstreet follow, and at the Battle of Second Manassas, a battle fought on as even terms as Lee ever gets, he decisively defeats Pope and brings the Union war effort in the east to its nadir.
Obviously Lee's failures in the Maryland and Pennsylvania campaigns will be brought up here, and justly so. I'll be happy to critique both campaigns to some extent. However, the main point I would make here is that Lee embarks on both campaigns for entirely rational strategic reasons. His biggest mistakes are, in order, giving battle at Antietam at all instead of falling back and conserving his troops after having mounted a very successful raid, and in committing to a battle of annihilation at Gettysburg when the time for such a strategy had long since passed.
This is where I think Lee's faults should be brought up. Lee could be overconfident and show contempt for the enemy's designs. This did not always result poorly, Chancellorsville is a great example where Lee cows Hooker into passivity by sheer audacity, but still Lee could have suffered a potentially fatal blow had Hooker stayed to receive Lee's final assault on his lines. Antietam and Gettysburg are two examples of this going very badly. Antietam was an unnecessary battle, the opportunity to escape was there, but he chose to stay and fight. Only his decision to stay one day after the battle salvaged some benefit to the Confederacy, giving his troops the impression that they had not lost. That said, it really did not compensate for 10,000 casualties and handing the Union a propaganda win. Gettysburg was, well, Gettysburg.