As I mentioned in my last post, most of the rules for 7th Edition are the same as they were in 6th. Even so, there are a lot of small changes that I think really benefit the game. Spoilers, but I don't think there are any that will make my Blood Angels work on the tabletop again.
1) The new psychic phase is the biggest deal. In the long run, it means that less powers will be cast each turn and that players will have to prioritize their powers and focus on the one that is important each turn. No longer can you cast every power you have just because you have them. Armies with access to only a few psykers (such as Space Marines) will still find them useful against most armies, though they'll be shut down by the really psyker heavy builds. It still remains to be seen if these psyker heavy builds will dominate the game or if psychic powers are too expensive and random to be worth the points investment.
2) Vehicles are harder to destroy with a single shot, which is great. Beyond that, transports became more viable. In 6th Edition, many of the damage results forced transported squads to snap fire. Now, they have to take a LD test, and fire normally if they pass. This means that your transported squads are way more likely to be effective when they reach the enemy.
3) Swooping Flying Monstrous Creatures can't switch to gliding and assault in the same turn. They have to glide for a turn before they can assault. While I realize that this weakens one of the few viable assault units, the ability to deliver a monstrous creature directly into assault with just about any target was very difficult for many armies (my Marines included) to deal with.
4) Locked Velocity is gone from flyers. I've never been able to figure out how this rule was even supposed to work unless you keep track of the exact distance that your flyer moves each turn just in case this result comes up. Now it will either crash or be stunned. Much easier to play.
5) Jink works equally for all models now, so bikes and skimmers have to consciously decide to Jink and then can only snap fire. This makes bikes less of an obvious choice over infantry, so maybe now we won't see so many Marine Biker armies. It also weakens Wave Serpents a bit, and I'm all for that.
6) Challenges are much more open now. If your character kills his challenger, any extra wounds spill over to kill other members of the enemy squad. If one of the challengers doesn't have a squad, the rest of the enemy squad can still beat on the challenger. This makes challenges much less of a tactical choice to tie up enemy squads or slow down an enemy combat character and more of a fun, narrative element.
7) Multiple barrages are much faster to resolve now. Most people didn't even do it correctly last edition, as the models killed had to be removed based on the positions of each individual blast. With a Thunderfire or a Wyvern, this took forever. Now, the casualties all are based on the center of the first blast. Much faster and easier to keep track of.
Those are the main changes that jumped out at me. What changes are you excited about?