The rocket boots are at once the best and worst additions to a Crackdown game I can imagine.

Pros:
Duh- they're rocket boots.

Cons:
They break certain aspects of the game.
No longer do you need to anticipate each new level-up of your agility skill so that you can go back to earlier parts of the game and go places you couldn't before... you just sort of rocket up there.
You don't have to be that careful as you climb or walk on high ledges- if you fall you can just rocket back up.
Driving at even 100 miles an hour doesn't really compare to having rocklets on your feet... so I hardly ever find myself driving- one of the greatest pleasures of Crackdown 1.
Until you level up your character- the rocket boots take up your grenade/utility slot. So no grenades. I mean, you can choose grenades... but how then would you use your rocket boots??!?

Combined with the wingsuit, it really is a very satisfying way to get around. Actually you have to throw the helicopter in there too. Compared to the first game- where verticality was an element, but you were always pulled back down to the ground-it's really great to be able to take to the skies in so many ways...

But I wish I hadn't had the boots since the beginning. They're part of a DLC pack I bought before I played the game (when it was on sale). I could just choose not to use them... shyeah riight.