Generally speaking, the cheap decks people start the game with aren't very interesting to pilot. They don't have enough removal, which is one of the primary ways players interact with their opponent's board. They definitely don't have boardwipes, which means just playing the best creature in hand each turn is usually the right play. They typically don't have much card selection. And most complexity is concentrated at higher rarities, so these decks tend to have simple cards.

That's not to say that all cheap decks are boring, or all tournament decks are interesting, but cards like, say, Duskwatch Recruiter, Dromoka's Command, or Despise, for example, just offer more choices than Craw Wurms or Grizzly Bears.

Regarding what others have said:

Damage not going on the stack was a good change IMO. Sacrificing Mogg Fanatic was always the right play; now it's less obvious. I agree with akud on detention sphere vs. O-ring.

Hexproof over Shroud was a mistake; with that said, they seem to have figured that out, and we're getting cards like Pristine Skywise or Dragonlord Ojutai instead.

I'm sad to see Protection be replaced by Indestructible. Morph/Manifest and DFCs show that they're not entirely shying away from complex mechanics.

What about the spell stack ? I seem to remember a LIFO spell stack for all instants and abilities, but now it doesn't seem to work that way ... I can't really tell how instants vs. interrupts work anymore and if the spell stack actually works the way it did in the old (late 90s) way ?

Or is it still the same ?

The Stack was introduced in the 6th edition rules change (1999) and still works the same way today. The 6th edition rules also unified the instant and interrupt types, because the separate interrupt type was only necessary in the old "batch-based" system.

The modern stack is so much more sane than the old batch based system. You can still do plenty of interesting things with it, like casting Blessed Alliance during the end of combat step to get rid of Giest of Saint Traft, or casting Infernal Tutor, then holding priority and cracking a Lion's Eye Diamond, or responding to an O-ring trigger with another O-ring for a permanent exile, or burning somebody out in responding to a lethal mana-barbs trigger.

MaRo started a "New World Order" (http://magic.wizards.com/en/articles/archive/making-magic/ne...) design approach in 2011, where they try to manage some of the complexity by making commons and uncommons have less and/or easier abilities. It sound reasonable, as casual players have a lot more commons and uncommons than rares and mythical rares, and it makes learning/enjoyment curve much less steep. Some experienced players associate NWO with "dumbing down the game".

I mean, that sounds infuriating to me, because it means to get complex effects you have to go and buy rares and shinies on the secondary market. I guess that was always the downside to playing a CCG rather than a straightforward tabletop RPG, though.

For me, damage not going on the stack was a big change. That's probably better for the game, but eliminates a lot of tricks.

Also, the cards printed these days tend to not allow you to hose yourself. Take things like detention sphere, that say "exile a non land permanent you don't control." It used to be that those types of cards would exile any non land permanent, do a skilled opponent could, in certain situations, exile something you controlled by bouncing their only non land permanent in response.

Removing damage from the stack actually makes the game more complex. Previously, it was always correct to stack damage first. There was zero penalty. If you knew the rules then you got to make the optimal choice.

Now you actually have to choose. Do I want this creature to deal damage or do I want to get the benefit of some effect due to sacrificing it or whatever. Sakura-Tribe Elder got worse but it got much more strategically interesting.

I stoped playing right around the time this change was implemented. What I felt back then was that while you are right in principle, in theory what happened was that the power level of a lot of interesting cards dropped so much they weren't playable anymore. So while my Mogg Fanatics got more complex, it didn't really matter because at that point I had to drop them from my deck, usually replacing them with something more dumb and mana efficient.

See also the replacement of Shroud (can't be targeted) with Hexproof (can't be targeted by opponents). There's no longer an interesting trade-off where you're sacrificing flexibility by being unable to target your own creatures.