I'll also observe that much of the criticism I've read of Enterprise is that it leaned too heavily on the previous series despite being a prequel, so Archer's crew faced off against the Borg and the Ferengi, both races that the Federation had never heard of or seen, respectively, in TNG. Considering that Voyager was content to retread TNG, I suppose this speaks to a broader sense of creative ennui on the part of the showrunners, but that's just idle speculation on my part.
The Borg could have been done a lot better than the episode. You'd turn them back into the nightmare they were from "Q Who?", and this nightmare only comes from pieces of Borg technology, rather than a full Borg ship.
I.e.:
1) Archeology crew at the Borg Sphere crash site. Lots of stuff is damaged, pieces, etc. They are using a fusion powered 747 or Antonov cargo plane that takes in air at the front, heats it up via fusion power, and spits it out the back. Lots of thrust, endurance, but only works in atmosphere.
2) Borg tech gets reactivated and assimilates some of the archeologists
3) Earth Space Command detects the aircraft leaving atmosphere. Attempts to contact are ignored, so local interceptors are scrambled
4) Borg modified airplane goes to warp. Earth Fleet notified, and due to the ship's speed and bearing, only the Enterprise will be in position to intercept.
5) Enterprise tries to intercept. Archer is not worried by scans of a weapon on board, as it only has enough power for 3 shots. He tells Engineering to use their warp field to bring the captured plane out of warp.
6) Borg airplane scans Enterprise, and fires the 3 shots. The shots have feedback effect along the polarized armor, feeding back into the engine core, causing Enterprise to drop out of warp. Borg drones beam aboard to grab a hydrogen fuel cannister to replace the fuel expended going at warp. The Borg ship does a very basic hail (so instead of the mass of voices, we only have 4-5)
7) Enterprise repairs the damage and gets back underway, but much better prepared.
8) Borg airplane intercepts a freighter, to gather fuel, spare parts, and extra crew. It also takes the opportunity to better reshape the craft to travel in warp.
9) Enterprise comes alongside, and begins sending people over to the Borg ship to scan it. Several cases are done where Trip mentions that a certain item is critical to the power systems, then that item powers down and is removed (Borg upgrades removing lower-tech items). Have a few comments about the Borg are increasing speed each time.
10) Archer decides to plant explosives to force the Borg ship to slow down, to talk to the Enterprise so they can meet the new race. This is a hostile act, and the Borg respond in kind. Several red shirts and a main character are killed. Two Borg drones are destroyed, and two red shirts are taken on board to replace them.
11) Enterprise and the Borg ship break off from each other, both badly damaged, the Borg ship actually in worse shape. However, the Borg ship is repairing itself faster than Enterprise, and heading back towards the freighter. Enterprise has to go after th eBorg ship again, eventually defeating it, and destroying all the fragments, then towing the remaining debris into a local star.
Key things:
1) The Borg are dangerous! Even a 22nd century airplane with a fusion reactor was able to attack and nearly destroy the Enterprise (antimatter powered with nuclear weaponry), thanks to Borg technology.
2) At least two main characters die. This reinforces #1.
3) The Borg tech has to remain hushed up, so nobody else tries to reverse-engineer it. This is why Ent-D never even knows about it (better if the records are stored at a secondary location that is destroyed in the Earth Romulan War).
I want the Borg episode to be where the viewers genuinely worry if the Enterprise crew is going to live, let alone win. Everyone watching this will know that "Here be Dragons" and they travel in cube-shaped ships.