I've seen a growing trend in new blocks for card (particularly creatures) to become more and more powerful. Years ago -- even as late as Ninth Edition -- Serra Angel was a rare, yet now it's an uncommon, and in its place is Baneslayer Angel. Leviathans have always had massive set-backs -- Islandhome, Untapping only at some ridiculous cost, etc. -- and now we have Stormtide Leviathan, which not only gives you an 8/8 for 8cc, but has numerous other upsides to it. And don't forget the Eldrazi, Goblin Guide, Bloodbraid Elf ....
I guess my question is: do you ever think that new blocks are getting TOO powerful, or that the aggressive curve is getting out of hand?
A: From Aaron Forsythe, director of Magic R&D:
Creatures have gotten noticeably better over the latter half of Magic's lifespan, that's for sure. Two things are going on: one, creatures were not given the correct power-level to adequately compete with spells for the first several years of the game's lifespan, and two, as we make thousands and thousands of cards, we need to keep people excited.
Serra Angel (and Hypnotic Specter) began life as uncommons in Alpha and were eventually both "retired" for being too good around the time of Fifth Edition. Former Director of R&D Randy Buehler came to the company around the time of Invasion development and helped show R&D the errors of its thinking—creatures weren't good enough! Randy reinstated some of the old favorites and started pushing larger creatures like Kavu Titan and the Invasion Dragons to try and get expensive creatures into constructed.
Since then, we've pushed the power of cheap creatures as well up to where we think they belong; after all, one way to get midsized creatures to be good is to make good fast decks for them to prey upon. Ideally the game contains creatures that are just as powerful on a card-by-card basis as things like Wrath of God, Lightning Bolt, Brainstorm, and other top-tier spells. Spells shouldn't always be the best cards in the game, which they were for many years, especially when cards like Necropotence, Mind Twist, Balance, and Counterspell were being printed and the creatures weren't any good. Environments like that make creatures feel lame and weak, when they should be the centerpieces of the game.
To my second point, we want each new set we make to seem exciting, so we try hard to make the cards look amazing. Sometimes this is done by making something actually more powerful than other iterations of cards in the same space—it is hard to beat Goblin Guide as the best aggressive red one-drop. I think that's fine to do here and there—after all, we don't want it to be true that the best cards Magic will ever have all already exist. Mostly, though, we just try to make things splashy, have them do things cards haven't done before.
In other words, I think we want it to look like there's power creep when there really isn't.