When I first started playing the game I immediately took a liking to the Stormcloaks, and my view was that these were "honorable rebels fighting the evil oppressive Empire". After playing the game for many hours though I started realizing that this was not really the case, the Stormcloaks were generally racist, brutish bastards. Ulfric comes across like such a man, while the Jarl of Whiterun seems much more reasonable. Generally most of the Jarls who support Ulfric (or take over if you side with him and conquer the Imperial controlled lands) are unsavory fellows.
- Dengeir is a paranoid loon.
- Korir is biased against mages and incorrectly accuses them of Winterhold's disaster.
- Skald is a hard-liner who comes across as an intolerant bastard towards his ex-legionaire citizens.
- Vignar Gray-Mane, whom I originally thought was a good guy, turned out to be a vindictive and heartless leader who allows his troops to harass non-Nords and mug / steal from his rival family (Battleborns). Some of the battle-borns are unsavory fellows as well, but I expected more honor from Vignar honestly.
Meanwhile many of the Imperial-side Jarls seem like good guys, such as Balgruuf, Brunwolf etc. Their viewpoint is not that the Nords should unconditionally bow their heads to the Empire, but rather that it's better for everyone that the Empire stay intact. The Nords were one of the people who founded the Empire, and breaking it up would just play into the hands of the Aldmeri Dominion. They want for the different people of the realms to work together basically, while Ulfric wants nothing to do with anyone but Nords.
The Stormcloak argument is that the Empire forced them to abandon Talos worship. The problem is, that really isn't the case. The Empire was forced to do this by the Aldmeri Dominion.
Ulfric killed the High-King simply because he could, based on old laws of the land (i.e. survival of the strongest, if you challenge someone to a duel they must accept). This is a rather barbaric tradition that favors brute strength over sensibility. I could overlook this if he really had a case against the Empire, but it seems to me from playing the game so far that he really doesn't. I don't see much evidence of the Empire oppressing Skyrim, in fact it seems to be fairly autonomous, the decisions are mostly made by local Jarls. The only exception being the Talos worship issue, and that was forced upon the Empire by the real bad guys, the High-Elf Empire.
In conclusion, I was a bit disappointed that I was pushed into siding with the Empire later on in the game, thereby stabbing the characters I met in the beginning in the game (which I liked) in the back. But I just couldn't let Ulfric win the war in good conscience, it appears that he and his chosen Jarl underlings would have thrown Skyrim into a dark-age and they would have become much more brutal oppressors of the people than the Empire was to begin with.