SR1 was a good game. The problem is that SR2 outdid it in just about every way. It doesn't make 1 bad or boring or whatever. It just means that 2 is better, and isn't that what a sequel is supposed to do, outdo its predecessor???
Now 3 is a mixed bag. It has better gameplay than 1 or 2, and sometimes more imaginitive missions, but it has less overall content, and most SR fans hate what they did with the clothing system in 3. They overhauled it when they didn't need to. As for missions, 3's good missions are GREAT, but there are fewer of them and just less content overall. Thinking back on it now, I can kinda tell how THQ's money problems affected that game.
Game to game, 2 is the best of the lot. It has the most content and is probably overall the most fun. I liked 1's story the best, and as I said, 3's gameplay was the best, but 2 has the best balance between them.
If I were giving advice, I'd say play them all in order. That way, you can get that 'in your face-ness' that 1 had, you can see the improvements from 1 to 2, and you can appreciate both the good and bad of 3. All in all, it is an excellent series, and well worth the purchase price (I paid full for all 3 and don't regret it). It really is the only legit challenger to GTA, IMO. It actually bests GTA in some ways. God help us all if Volition ever got the same budget to do a SR game that Rockstar does to do GTA...
Alabama Crimson Tide: Now serving title #15.. ROLL TIDE ROLL!!!