I feel like I've totally missed out on SR2... The first one was so blah and meh back then, I had zero interest in SR2. Wasn't even gonna care for SR3 until it was free on PS+ and bork insisted I play it... I did and totally had one of the biggest blasts in my gaming memory... I had no idea.
If you thought the first one was blah I dont know why you would like the second one
1 was better than GTA IV in a lot of ways
First one was a bunch of guys in Champagne, IL, making what they thought was gangbanger GTA game, without a sense of humor. They studiously avoided several GTA gameplay mechanics, likely suspecting it would awaken something litigious in Rockstar.
When GTA IV finally came out, it abandoned all the R3 side missions that made the PS2 era games so fun for many open-world enthusiasts. Volition seized on this and made SR2 largely based on side missions AND made the game fully playable in Co-Op, which any network engineer can tell you is a remarkable feat. (It unfortunately launched with a shit-ton of bugs.)
Elsewhere in this thread, it was mentioned that Gat Out of Hell also re-used the SR2 or SR3 maps, but I do not recall this being true. Some assets may have been re-used, but the map itself was a hellscape which required a number of vertical traversal gameplay additions.