The gameplay is exactly like Xenoblade, with some clear additions and modifications.
The gameplay is fundamentally similar to games such as Dragon Age Origins, Final Fantasy XII, or World of Warcraft. In short, a combination of a basic auto-attack with various special powers that need to cool-down after you use them. All that slashing and shooting in the trailer? Most of it is just simple auto-attacking. The mech's right hand rifle shooting is also an auto-attack.
In the trailer, you can see the player controlled character use several special moves: a multi-hit flaming sword attack, a rising spin slash, a move that imbues his sword with fire to grant some kind of self-buff, and a healing move with he gun. In the mech, the shoulder mounted missiles, arm mounted energy shield, and sweeping Gattling-gun attacks are also special moves on cool-downs. For all of these, you can see the buttons to trigger the special moves, and the cool-down timers at the bottom of the screen.
Now, another mechanic X seems to be borrowing from Xenoblade is the timed B button press seen in the center of the screen. In Xenoblade, this is something that was triggered by events such as starting a battle or a party member getting a critical hit, and timing the button press correctly would give the party a morale boost or raise affinity between party members. In X, the button presses correspond to similar situations: starting battle, hopping into the mech, or knocking the large enemy off-balance. However, in the trailer it appears that a properly timed B button press heals the party for a small amount of damage.
What made Xenoblade so great of game was how great the design of the character special abilities and traits were, and how good the character customization was. You had characters built to be tanks that you could repurpose into killing machines, and even healers who could use situational instant-kill headshots. You could give mages who normally use light armor the ability to use heavy armor and gain unique benefits from that. Every character had several different ways to build them thanks to a mix of equipment, different abilities you could set, linked skills, gems, and so on.
On thing that X is definitely inheriting from Xenoblade is an emphasis on positioning during combat. In Xenoblade, certain skills could do more damage if you used them from the side or from behind an enemy. Now X even has a specific display on the lower-right of the screen that specifically indicates whether you are standing in front of, to the side, or behind the enemy. And I believe that the flaming combo slash did bonus damage based on position. You can tell, because like in Xenoblade, the damage indicator had a spiky yellow box around it when you do bonus critical damage.
What is even more interesting is that in X there is a small green circular indicator on the limb closest to the player. This indicates the existence of limb targeting system, and limb-specific damage, a feature implied by the limb-severing shown in earlier trailers. This would be a system wholly new to X, compared to Xenoblade. It reminds me of similar targeting used when fighting large opponents in White Knight Chronicles, but in X it is applied to smaller opponents as well.
Another change from Xenoblade seen in X is implied by the last part of the trailer, where the focus character hops out of his mech and enters some kind of special attack mode. That mode seems to resemble the chain attacks from Xenoblade, but it is somewhat difficult to make sense of it without more context. However, the fact that they possibly changed it from a system where time stops in Xenoblade to one that remains in real-time in X is further evidence for a multiplayer element in X.
And I think it is safe to say that X is a multiplayer game. Of course, that doesn't imply anything about the existence or absence of a complete single-player story in X. I think the presence of cutscenes and large towns in the earlier trailers, as well as the history of this developer, would point towards this being a game with a fully fleshed out story and single-player gameplay.
Another detail that points toward the existence of multiplayer is seen in the status window of the party. All four players have wildly differing levels, but are all listed at Rank 10. It is hardly definitive, but it is possible that Rank indicates a certain degree of multiplayer progress, which is kept separate from level. It isn't possible to figure out what this means with just this trailer though.
Overall, X is shaping up to be exactly what I though it was going to be from the early trailers: Xenoblade plus mecha and multiplayer. That is exciting and interesting, considering how great the gameplay in Xenoblade is.
EDIT: Oh, I forgot one detail I noticed: you can see a red eye indicator next to the name and level of one of the enemies. In Xenoblade, such an indicator marked that the enemy would aggro if it sees the party. Other enemies would aggro based on sound (moving too quickly near them) or would specifically aggro if another nearby enemy aggroed.
