5e vs 3.5?
5e is ultimately simpler, but with a looser rules system. It requires more GM interpretation of the rules, and isn't as solidly written. This is a feature, not a bug, but some people don't see it that way.
5e is less mathsy across the board, with fewer buffs and the like. There seems to be less "you get +2 from here, +1 from here, and another +3 for here". It doesn't have the OotS joke - "he'd be a great fighter if he had a better head for math". Combats seem slightly quicker, but not as much as some fans express.
5e has shorter buffs when they show up, and save or die effects tend to only last a few rounds at most. Characters get hit more, and take more damage, but are less reliant on heals and all that. Whereas 3.5 was about the game on an encounter level, 5e takes a more "adventure" approach, what with the short rests. 3.5 seems to be balanced towards 3 or 4 encounters a day. As indicated in the DMG, 5e aims towards 6-8. I'm not entirely sure if this is true, but personal experience shows that 5e adventuring days last longer than the "15 minute adventuring day" issue I saw back in my 3.5 days.
3.5 was definitely more granular. You had a lot of skills for specific things, feats for specific combat maneuvers, and ways to improve/modify every character ability. Want to improve your initiative? There's a feat for that. Like to trip? Feat for that too. 5e, on the other hand, doesn't really work that way. A lot of skills that we saw in older editions (such as riding) kind of get handwaved. If your background supports doing something that isn't in the rules, you can usually just do it, or the GM is expected to make a rule up on the fly.
Combat in 5e is a little less swingy than 3.5. 3.5 tended, especially at higher levels, to have an awful "swing until you crit" mentality - crit-fishing was a pretty valid tactic in 3.5, combined with power attack. In 5e, crits are powerful, but not nearly as much (even with sneak attack dice being doubled!). The fights are less swingy towards the PCs as a result. On the downside, the PCs in 5e have a pretty strong ability to steamroll enemies. Boss fights in 5e seem less reliable to stage effectively.
Honestly? I prefer 5e, and that's where my bias lies. I really don't like 3.5/pathfinder, and haven't for years. I think gaming should be simple, and that rules wind up being impediments to play. that is where my tastes like, and so, expectedly, I'm not much of a fan of the legalese texts that were in vogue in the 3e eras.
If you do it try it out, have fun. As with a lot of things, it all depends on who you play with.