3.5 right now is like Magic: The Gathering - LOTS of options, LOTS of complexity, HUGE time sink before you can get into it seriously. There are LOTS of traps, LOTS of variance in power levels, and LOTS of things to track - even for simple* by-the-rules activities like fighting bandits or balancing or grappling.
5E right now is like an elegant rewrite of D&D 2E/3E/4E, combining the best aspects of each. It's simple, it's focused, and it's good at what it does. If you simply want to play a dungeon crawl/political intrigue/video RPG-like tabletop game, it's elegant and it generally works well out of the box. Lemme say that again: It works well out of the box! You don't need to make an Ubercharger to be a useful melee man. You don't have Enchanter Tim losing access to spell schools, thereby making him useless outside of his field of specialty. You also, currently, don't have a by-the-rules guide on how to make a Dire Ape Barbarian Monkey-Pony. Finally, you don't (or at least I didn't) have the amount of rules lawyering/rules bickering that 3.x/PF had. It's simpler, it's intentionally simpler, and it's a good thing for people who don't want to spend a solid week researching how to best optimize one character. 5E is also better suited for the expected audience - busy people - that is, people who want a life outside the game.
Sure, 3.5 is great to us, but that's because we've spent a large and important part of our lives and free time playing and discussing it and writing posts and guides about it. The typical* player? Just plays things he thinks is interesting and doesn't spend hours or days or weeks researching. He's here for a game, not homework.
On the GM's side, there's unquestioningly less effort required to make and run an interesting 5E campaign that doesn't spontaneously break or slow to a crawl due to the minutia. How much does it matter that 3.5's 'PCs and NPCs should be equal' philosophy matter when you rarely face the same creatures both out of and in combat? (Out of combat, social skills matter. In combat, fighty stuff matters.)
There's a good reason I'd rather be a PC than a GM for many 3.5/PF campaigns. I've done it. (I ran a campaign from level 1 to 21.) I could do it because I had 20-40 hours per week to prepare and play. Right now, I have other things that are of higher priority to me.
Finally, what's more important - the rules or the play? I had to learn this the hard way. Tremendous knowledge of and strict adherence to the rules in an environment meant for notable degrees of improvization when messing around with friends is often an obstacle to fun. My campaign that ran levels 1-21? I didn't use the rules to their fullest. I didn't try to exploit every little edge I could. I just went with a general knowledge of what would work, told my story, involved my friends (and myself!, and we all had a hilarious, good time over the span of 16 months.
The rules exist to facilitate play, not to replace it!
(*Subjective)
