I haven't played as soldier myself, so I can't speak for how fun the class is to play as. I know that playing with biotics and tech powers is really fun. As for the difficulty, normal was very easy when playing as a vanguard and I never needed to learn how to break down enemies because brute force worked. Soldiers have different ammo types that have different effects on shields/armor/health/etc. For instance, the incendiary ammo is useful on Krogan enemies because it stops their health regeneration.
My guess is that playing as a soldier on normal is more like playing a regular shooter (like Gears or Uncharted), which is still enjoyable in it's own way. But that is only talking about Shepard's combat skills; you will still have control over the actions and powers of your team. So if you choose to be the tank Soldier, you can go with one biotic squad member and one tech one to balance it out. That doesn't mean that a biotic or tech based squad member is as good as you would be if you took that role, but they should keep you covered for the different enemy types and situations. If you played as a biotic, you could curve powers around and over cover. If you played as infiltrator, you can go invisible, flank the enemy, and snipe them from behind. I understand soldier has a bullet time skill, so that could be good too.
The good thing about ME2 combat is that each class is very different to play as. I think it really helps make it a replayable game.
