You get fantastic spells, bonuses to sneak and illusion, strength bonuses. The only downsides are that you can't go in the sun and people attack you (fire damage is nothing to me), but you can control your level very easily if you just feed, which is not difficult. Especially if you remember to use that handy invisibility power it grants you.
People constantly compare Vampirism to Lycanthropy. They say that Werewolves are better simply because there are no negative effects. Well they aren't being fair. You can only get those bonuses while in your werewolf form, at which point you're attacked on sight (sound familiar?). Vampires however can have their full bonuses available to them throughout an entire dungeon. Don't think that I'm saying vampires are better, because I'm not. I'm simply saying that they are equal, and neither is better than the other. However playstyles may favor one to the other.
It's extremely easy to feed every day or two while in the city, then stop feeding when you want to fight a dungeon.
[Though I will give you one thing. Having to manage yourself to have a follower does svck]
I agree with you--I definitely don't hate--but what spells and "strength" bonuses? All I know of are the unique absorb health spell (which isn't affected by any perks, and I personally do not find it useful) and Night Eye, which is only useful for non-Khajiit (and everyone knows all the best players ever choose Khajiits). Beyond that, everything else is leveled and can only be used once a day; illusionists and conjurers also have better spells (invisibility can be cast while invisible to circumvent the enormous 180 second timer the vampires get after not feeding forever).
Still, I find being a vampire awesome under the right circumstances. It's too bad it's not as great as in Oblivion, where you would get bonuses to Blade (One Handed would be nice) and you take Sun damage outright instead of just being nerfed in sunlight. I think that was awesome because it forced powerful vampires to either consistently heal or, if they've not fed for a long time, to not get out during the day at all. I couldn't resist being a vampire in Oblivion

Edit: I mean bonuses to a set of skills overall as well as attributes. It could have been done in Skyrim: better health regen after feeding until you get hungry again, fortified stamina and certain higher skills (like Destruction!), etc. I think it'd be nice; I at least want my Destruction bonus back.