I ultimately remain unimpressed by 200m hills. I mean you can find similar hills in southern poland, and perhaps make a case for them slowing the German offensive in that region, but they hardly crippled it:
http://upload.wikimedia.org/wikipedia/commons/6/62/Poland2.jpg
I admit that trying to crack the Carpathians is a world apart from invading Bessarabia. I can agree that a successful defence of the Carpathians could quite possibly be attempted. The issue however is that, from the Soviet side, there is no reason to do so, as by avoiding the Carpathians you effectively take everything in Romania worth having and so should reasonably be able to force a peace treaty or install a puppet regime if that is your intention.
And yes, I suspect the fighting will be bloody. Yet while it may tend towards a "WW1 type blood bath" battles in WW1 could still be successful, armies could be routed and ground could be taken. If the Soviets suffer a couple hundred thousand odd killed, wounded or captured and the Romanians suffer a couple hundred thousand odd killed, wounded or captured then the Soviets are bloodied but hardly wounded wheras the Romanian army will have been crippled as an effective fighting force.
In order to get the "Winter War effect" you need Romania to inflict several hundred thousand casualties and yet get off relatively lightly herself. While the Winter War would still be notable, the effect I think would have been rather different had Finland been bled white in holding the line before eventually capitulating. Such is likely to be the situation in Romania.
The clear differences with Finland are as follows:
1. The weather is better. Obviously this is sort of dependent on the time of the invasion, the weather could have been alot better in Finland had Stalin and co decided an invasion in the depths of winter would be somewhat unwise when the target could fall far more readilly in a few months, but there seems little reason that the Soviets must wait for the depths of winter to attack here.
2. In part because of the above the logistic situation for the Soviets is far better. They shall be able to make far more use of mechanized forces (although the bulk of their forces shall still be on foot) than they did in the Winter War when such was rendered almost non-operational.
3. The big one to my mind, the front is far larger. We could debate the real effectiveness of the Mannerheim line, but it was ultimately defending a stretch which was only some 100km across. The other lines of attack were relatively easilly contained due to the climate rendering logistics almost nonexistant. Taking your own map just from the Black Sea across Moldova you have a front of some 300km, the actual figure that has to be defended (since Moldova is smaller than the entire area) is probably closer to 400km or so. True the Romanians could do something to narrow this front, by falling back to the Carpathians, but doing such effectively surrenders the area the Soviets desired anyway.
All three together shall make the key Soviet advantage, that is greater numbers, far more effective than it ever was in Finland. If a Romanian division finds itself under attack by three Soviet divisions then, while it may give a good account of itself, it is still going to be mauled.