Haha, superb. That could be used extremely effectively in maps like Well where the enemy he's making invincible could stand up on the upper levels while the medic stays safely out of sight.
The gameplay's definitely being modified, as from what I saw the Spy now gets to go temporarily invisible instead of being permanently disguised as an enemy. Whether this is an improvement or not is up for dispute, and I don't think that kind of thing gives the game more depth so much as simply changes the formula.
TF2 will probably be great as I said way earlier in this thread, but I think the removal of grenades will take a side of the game away that a lot of people will miss. Play CS:S? Imagine them taking out automatic weapons. Battlefield? Imagine them removing vehicles.
That's how frequently the various types of imaginative grenades were used by past players of TF. Battlefield and CS:S may still be great fun without those elements in place, but they sure wouldn't be as dynamic nor as varied in the long-term.
I hope I'm managing to make those of you who never played the older TF iterations see our perspective.