Wow, I spent 40 hours playing this game. I guess I liked it!
Luckily I read a review before I played that said to go slow thru the story missions, and do a lot of the secondary tasks in between main tasks, and I'm glad i did so. The secondary tasks have a very addicting quality to them, especially once you get the hang of how the enemy AI works, where you just want to keep going for hours. This is great because once you clear them out, they are gone forever, earning you money, and making the main story tasks easier when you get around to doing those tasks.
The main story tasks I thought were great. Plenty of checkpoints, and since your world progress is saved separately from your mission progress, you don't have to re-do much to get back to where you were if you were killed. I really liked that dual saving, and wish more games did that. I just wish it has some more main story tasks, those being the best part of the game.
The character movement was the main drawback - very stiff and not very smooth, especially I was just coming from playing Assassin's Creed 2 before this. His stupid sayings really started to get annoying after 40 hours.
But the arcadey gun battles and blowing stuff up really was a lot of fun, I had a great time with it over the 40 hours. Even now as I write this I feel like jumping back into the world and continue with those hundreds of secondary tasks, which mostly involves blowing stuff up.
In summary, if you like open world games with lots to do and see, then you should get this - especially now it's so cheap. Really great, and maybe one day some other developer will pick up the story.