Lots of Fun, but Technically "Meh"
Good team-up books are fun. The whole point is to have your favorite characters from different books interacting in neat/unexpected ways. In that sense, X-Men #16 is a home run. I had a lot of fun reading the way that the FF and X-Men interact. Superheroes are always so snarky to each other. You'd think they'd be nicer to people who have saved their hides a bunch of times, no?
Oh, I know it's nitpicky to complain about the way an artist draws a character, but Jorge Molina just doesn't cut it on a few for me. Emma and Sue both have close-ups for punchlines that are just no good, Spider-Man's physique is absurd at the start, and Sue's elongated neck in the Doom "wham panel" makes it look like she's the one with stretchy powers.
The rest of his art is great. Bright, colorful, and clear, but he's just not good at normal, unobstructed human faces (to me, at least).
The workable art combines with Victor Gischler's over-writing to make for a book that is certainly fun to read, but ultimately flawed. I've complained about this at length in Dan Slott's ASM, but writers should trust their readers and writers a little more. You don't need extra dialogue after a joke to explain the punchline. Sometimes a reaction shot can be way more effective.
I still think X-Men is a fun enough read to be worth the cover price, but don't expect to be blown away.