I love the new Alterac Valley. The reinforcements mechanic is excellent.
In my first game (as Alliance), we swept down to Frostwolf Village in an old-school rush. It did not work out well, as the Horde recaptured the towers and graveyards behind us, and the waiting defense shredded our offense. So we went back on the defensive, but that ill-fated attack put us behind by 100 points or so. Finally, as the game wound down, we were losing 40-150, when our second offense managed to punch through and kill Drek'thar. It was a great, nail-biting game.
The best thing about the new AV is that healing feels so much more worthwhile. Intellectually, I know that healing is quite powerful, and keeping my team alive is the best strategy, but the cost of death used to be so low that it was hard to really see, especially when I could have more fun swinging a giant hammer. In the new AV, every player I save from death is another reinforcement that we have. The cost of death has increased, and that makes healing more valuable.
The new reinforcements mechanic would go very well with Warsong Gulch. If WSG had about 50-75 reinforcements, it would stop the stalemates that drag out forever. In general, I do think battlegrounds need a time-limit. Having alternate paths to victory is also important, as it allows you a variety of strategies, but one of the paths should be a time-limit. The reinforcements mechanic is a good one, as it increases the cost of death and makes people play more strategically.