It's difficult to evaluate Rise of the Eldrazi, because we're simply not used to SEEING so many spells costing that much. How can we evaluate a 10-cost spell? And how about a 15-cost spell? Is it possible to CAST them? Yes. Is it likely? No, not really. Can you design a deck to do it? Yes. Can it win? Probably not enough to warrant attention. Can you use Eldrazi Spawns? Of course. And lose to Jund Charm, Volcanic Fallout, that black sorcery with kicker I forgot the name, Infest etc. SOME of those giant spells will see play, for instance, I think giving red and black a way to FINALLY get rid of enchantments is worth the 7 mana in a slower environment. However, this set has everything to go poorly. As for level up, MOST of the levelers suck, but there's a blue Merfolk that flies early that seems worth it, and there's a white weenie guy that is good enough. Not superb, but good enough. In Extended and forward, Serra Avenger outshines him too greatly to even consider. There's also a nice red aggro dude,
RR for a 2/2, he fits nice enough in the curve, and you can level him up on turn 4 and again on turn 5, all the way to go toe-to-toe with Figure of Destiny. However, he's WAAAAY less versatile, and if I'm playing monored, I need to be more aggressive than "drop a bear, do nothing on 4th turn and hope for no removal, again on 5th turn and THEN you might win". I want to be WINNING on the fifth turn.