1-The 8 lores of magic changed significantly, and got more powerful.
2-The effects of a miscast got allot worse.
3-Wizards can only use their own power dice and those in the pool to cast spells. They can no longer take other wizards power dice. Dispel dice are still a common pool.
4-You no longer panic if a fleeing unit goes past you. You now only panic if a unit of unit strength 5 or more flees through you.
5-If you overrun an opponent into an EXISTING combat, your attacks take place this round, not next round.
6-All panic, terror, etc.. tests have been standardized to 6".
7-Independent characters can always be targeted, even if within 6" of a unit, unless they are in a unit with at least 5 other models.
8-Units in combat are immune to psychology
9-Great weapons are +1 ST when used mounted, +2 ST on foot
10-Skirmishers now get marched blocked like everyone else
10-The way chargers are moved and units 'slide' to maximize changed slightly.
Of course, don't go out and buy 7th edition. GW in its 'great wisdom' has decided to release 8th edition this summer.
PLAYS: Daemons, Tomb Kings, Beastmen, Chaos Warriors, High Elves, Wood Elves (fantasy), Imperial Guard, Adeptus Titanicus (Epic), Eldar, Craftworld Eldar (BFG).