XXI sure is amazing! Every spec of it is far superior to everything you've used to and in that sence makes the VII- and IX-line feel like submersible surface boats rather than submarines.
Speed both surface and underwater, diving speed and depth, torpedo loading speed, camo capabilities... All amazing and nothing like before. Plus the best little gizmos German scientist came up like schnorkels and RWR, you name it you got it!
Then again it's late war and there's only so little single kaleun can do to sunk enemy ships and still survive. While having the ability to launch six acoustic torpedoes and reload all tubes in ten minutes or so, attacking convoys is pretty much a no-no. At least unless you're a very seasoned veteran and no excatly how to avoid the finest ASW devices aboard those destroyers.
In 1945 I believe U-boats stuck close to shores protecting fatherland rather than tried to sink merchants in Atlantic or Arctic ocean. While you most certainly can, the massive convoys are extremely dangerous to attack, and then again sinking rogue merchants on the coasts of England doesn't feel the same anymore at that point. The amount of airplanes protecting the seas north and west of British Isles is huge and makes the trip around boring since you have to (and should!) dive all the time.
XXI is a u-boot to experience of course, but would I take it on next time I play the war, I'm not so sure anymore. The feel of overpower makes me recless and attacking convoys recklessly late-war is a sure way to get sunk, excatly like JuanLiquid said! Then again this is in no way XXI's fault
