Only played one game (0-0 friendly between Barca and Milan) so I don't have any really in-depth comments to make, but I'll make a few general observations:
-Can set difficulty/style/controller configurations after the FIFA splash screen like on first boot in previous years (Beginner-Experienced-Advanced settings, which will determine difficulty and level of assists)
-Playable modes in demo are kick off (play now/exhibition/friendly) and a demo version of Ultimate Team (which I didn't try).
EDIT: Practice Arena is also available in the "play" menu.
-Other game modes are selectable, BUT display a menu screen describing the mode and its improvements.
-3 Minute half length for friendlies, which is unchangeable.
-Only match options that are editable are weather, difficulty, game speed, gameplay sliders and level of controller assists/controller configuration. Will check again later if anything else comes to mind.
-All (kick off/friendly) demo games are played at Camp Nou. Again, haven't tried FUT.
In-Game:
-Only going by one game here and I don't want to upset/disappoint many so I'll say it as generally as I can: if you loved the past few years of FIFA football, you'll love this year's game as well. Same may apply to if you disliked it. Default game speed, like last year, is still quite fast. Will play a match on slower settings to see how that compares (as that's the speed I played 13 on).
-Only played on the intermediate difficulty level with assists off and didn't notice any dramatic differences in AI. There have been some new animations added and a few things are a bit less wonky in the physics end, but nothing too dramatic.
-Presentation is among the best of any EA title. A new member of the commentary team introduces the game and the commentators. The studio host also introduces the halftime highlights. Martin/Alan have a few new in-depth lines to start the match. My match had a few longer asides about Neymar joining Barcelona and the Camp Nou stadium, as well as Barca's struggles during the Champions League and their "more than a club" philosophy "breaking down" with Messi out of the lineup. It was really informative to hear them talk at length about this and it reminded me of how NBA 2K handles its "storyline" commentary.
-Some of the "living worlds" stuff I saw in FIFA 14 next-gen Gamescom videos made it into the PC version, including cameras that follow the ball and walking stewards/officials. The "other game" had these small environmental details aplenty in previous iterations, but I don't recall FIFA having the same last year. Managers have been removed from the sidelines for some reason.
-Face models are both accurate and excellent for Milan and Barca, as expected (two of the most prestigious teams in the world and the starting 11 also received facial scans from what I recall).
-Small detail, but replays at halftime and full-time now feature information in the lower third:
Once again, my observations/impressions are all very general at this point. Let it be known that I also plan on purchasing next-gen FIFA and "that other game" instead of the current-gen/PC version. Thankfully, this version is definitely on par with the new current-gen versions of 14 and isn't a re-skin like Vita's infamous "Legacy Version".
Will reply with more observations the next time I'm able to play another quick demo game.