I love the idea of "A+X" -- standalone comics operating outside any continuity just trying their best to be great short story team-ups in a fun and entertaining manner. That said, telling short stories in comics is very difficult to do, especially when there's only half an issue to work with.
Dan Slott and Ron Garney take 11 pages to tell an almost sweet time travel story about Captain America and Bucky trying to thwart a young Trask from building a Nazi Sentinel. Cable pilots in (as he is wont to do) and the three team up for a quick takedown. Slott doesn't try to tell an overabundance of story in his pages and thus succeeds in telling a satisfying 11-page tale. He gets in a couple good jokes and the idea itself is fun enough. Garney keeps things very clean, which makes the storytelling nice and clear, and the poses and colors (by Will Quintana) are appropriately superheroic. There's not much meat or meaning, but that's hardly the fault of the creators.
Jeph Loeb and Dale Keown have even fewer pages (10) than Slott and Garney and it shows. Though there is absolutely some fun stuff between Hulk and Wolverine as they argue over cake, in the end, their future selves (or alternate timeline future selves? Who knows?) show up and it becomes confusing. The story doesn't have time to go anywhere, and is mostly baffling once the future selves arrive -- though Keown does manage some good action in his tiny panel time. Had it just been a hilarious story about cake, they might have actually had something. Instead, the story drags out into a larger cliffhanger that makes it difficult to care, as we have no idea if it will ever go anywhere.
Ironically, both stories each use a giant splash double page spread, which seems ill-advised given how few pages they have to work with. In the end, Slott and Garney's splash works because it showcases a big reveal (and because they have an extra page to spare) and Loeb and Keown's does not because it's just a giant "jumping into action" panel that we've all seen a million times before.
At the end of the day, I think price point is the biggest issue. This comic costs $3.99, which is just way too much money for what you're getting. Comparably, the same day, I bought "Batman: Li'l Gotham," which (even ignoring any quality comparisons) at 20 pages is nearly twice the size of either of these stories on their own and cost only 99 cents. Even though there wasn't anything horribly wrong with "A+X" #1 and the idea of the series in and of itself is fun, my comics budget is precious. I wouldn't buy this comic again unless it featured my absolute favorite creators or favorite characters (thus I will pick up "A+X" #3, which features Rogue and Black Widow by Chris Bachalo). However, I think that kind of reader defeats the very purpose of the book. The book should be super fun stories that allow readers to search out new characters they might not have otherwise known they'll love, but at $3.99 a pop, it seems unlikely to happen.