So I loved Saints Row 2 and have been waiting for The Third to come out ever since. How does it compare? Well - its similar but different; it keeps most of the good bits of SR 2 and improves on them and bins off the less good bits. There are a couple of disappointments, but I'll come to them later...
So the plot is fun - silly and occasionally jaw dropping. The second mission on the plane (I will say no more) is one of the most genuinely awesome gaming experiences that I've had; the gameplay was simple, but the visual effect... wow! Having worked my way through around two thirds of the main plotline, it is funny, kinda clever in parts. Not quite as engaging or dramatic as parts of SR2 (nothing to touch the SR2 Brotherhood plotline, certainly), but solid. Another nice touch is that, as well as the better graphics, customisation goes a bit further than SR2. As well as boosting your characters resistances and skills (with money, rather than by completing the minigames, with certain boosts locked until higher levels), you can customise your weapons to be better, including (in some cases) being able to shoot explosive or incendiary ammo.
One of the things I liked most about SR2 were the minigames and these are back in abundance - and most of them are a lot more polished and good fun than the ones in SR2. As well as the old favourites, there's also a version of Mayhem played with tanks, a survival maze where you shoot people dressed as hotdogs and a truly brilliant version of Escort which I won't spoil for you (but anyone who has seen Talladega Nights will love the reference). The tasks are all engaging but not of them are too taxing.
This touches on one of the issues that was a bit disappointing - the game difficulty (at least on normal) is very low. While this is kind of nice and means you don't end up playing the same tasks over and over again (like the higher levels of Trail Blazing in SR2), there isn't much of a challenge. Maybe the harder difficulty levels will be different.
Other good bits - better soundtrack than SR2 I reckon, less fiddly vehicle customisation, fun new characters (Oleg and Kinzi are both ace; Zimos is good in a quirky, Marmite-love-him-or-hate-him kind of way). Although some reviews elsewhere have criticised the cityscape as being too samey, I don't think this is the case; it isn't as varied as SR2, but that always seemed a bit over-artificial to me anyway. There is some variation, and it isn't as dull and samey as Liberty City in GTA 4 was.
Bits I didn't like - Shaundi has turned from cute stoner babe to Cheryl Cole semi-lookalike with a chip on her shoulder (although minus the Geordie accent) and the character is less engaging for it. There isn't as much out and out silliness in the same way that SR 2 had (fewer weird secret locations) and the gameplay isn't as rude or, for want of a better word, 'edgy'. This is played up to in some parts (when doing the minigame in SR3 that was, in SR2, drug dealing, your character is distributing naff Saints Row merchandise), but there is a definite feeling that aspects of the game have been toned down to avoid criticism. There aren't the same options to customise your cribs to the same extent either, which is a bit of a shame, but they're actually pretty sweet anyway so that's not so bad.
All in all - worth the wait and worth buying new. Great for dipping in and out of and playing casually, if you liked SR2 (and/or thought that the GTA series has started taking itself too seriously), then you should buy this game.