Woa, although SR:TT was great, it isn't top contender for Best Sandbox game, here are some reasons behind this.
1. No improvised weapons
2. No walking styles
3. Needs more clothing
4. Nickle and Dime dlc that is already loaded on the disc
5. No city interaction
6. Not enough buildings to go into
7. No clubs?
8. Activities as missions that should just be an activity intro
9. Not enough dialogue
10. Not enough guns!
The problem with your post verses mine is that I was VERY CLEAR to label my contention as my opinion, which I know many people share. You then contradicted me (which is fine) but are posturing as if all the factors you listed are some objective, unimpeachable criteria that cancel out what I said.
Now in your opinion they do, which is fine, but let's take a few of your points;
1. I completely agree with you about the DLC. It is completely anemic and overpriced, so I am with you on that one. However, it in NO WAY argues against the intrinsic game itself, which is complete without the DLC.
2. Clothes. What do you think this is, Barbie Dress-Up? Ha, I kid. I too miss the customization of SR2, believe me. But I DO NOT think that this in any way makes SR3 less of a candidate for best sandbox game. It is merely one issue that, to my way of thinking, is quite minor compared to what SR3 brings to the table that SR2 can't even touch.
3. Other points such as enterable buildings and clubs are, again, a matter of opinion. I personally don't care about entering buildings, and in fact, Just Cause 2, which I consider another candidate for best Sandbox games has almost no enterable buildings.
4. I think there is plenty of dialog and I am not too bothered by some activities masquerading as missions. Because there is so much to do in the game.
My point here is that, while the factors you listed above are very important to you, not everyone feels the same way you do about those things, and truth be told, the breadth and scope of SR3, in my opinion, just makes all of those points unimportant. Now this is not to say you should feel they are unimportant.