I tried one of the earlier Saints Row games and didn't like it, but I've been watching 2 of my favorite gaming commentators play IV in co-op on Youtube and it actually looks really fun. I might just get a copy.
As a person who plays both GTA and Saints Row I have to say that Saints Row is much more fun to play, and replay. Its ridiculous weapons/events/overall atmosphere provides for tons of fun. Other games, that take themselves too seriously, like GTA, simply can't match that.
I think it is a lot of fun, and even if they did try to be a GTA clone at first, they have acknowledged that was not the best route and have taken it in a completely different direction. If you are truly hesitant about purchasing it, Cracked actually did a pretty funny and well written article about why it's actually pretty great, might change your minds: http/www.cracked.com/blog/5-things-all-games-could-learn-from-saints-row-iv/
I've been watching a youtube gameplay channel too, theradbrad, tromp through this title. His gameplay is atrocious, but the commentary can be amusing at times... "oooh take it deep b!t@&" lol... anyway, the gameplay and controls look solid, the game itself is hilarious, but it does suffer from serious slowdown issues when the screen becomes filled with npc's, vehicles, explosions, etc.