Apart from the advantage system, 5e looks great and they brought back some great features from 2e that went away in 3-4e.
The problem is that advantage/disadvantage is too deeply embedded as a core mechanic in 5e to get away from it. Advantage and disadvantage is not nearly as subtle as a -1 to -4 or +1 to +4 penalty or bonus required based on certain effects. The old system allowed for fine-grained adjustments that scaled on a flat percentage. In the old systems, probability was predictable. Probability scales awkwardly with the new system, as the chance of success and failure in the advantage/disadvantage system is always multiplicative.
http://anydice.com/program/11fd
Top table is a roll 1d20 probability chart, average roll is 10.5 and chance of any one number is 1/20. With advantage, the average roll is about 14, the chance of a 1 is 1/400 and the chance of a 20 is 1/10. With disadvantage, the average roll is about a 7, the chance of a 1 is 1/10 and the chance of a 20 is 1/400.
Let that sink in.
Because having advantage is so very good, and having disadvantage is so very bad, it's actually unlikely not to encounter it with intelligent players and DMs controlling intelligent NPCs; advantage is pervasive by design. In my experience, players will be agonizing over seeking advantage at all costs, and intelligent NPCs should be as well. Play testing showed me that my group of players were so obsessed with seeking advantage that it detracted from the game-play.
If anyone has ever fought "pugwampi" in Pathfinder with their "unluck aura" there's a fine example of how a few well placed CR 1/2 creatures can totally wreck a PCs day in higher CR encounter, such as a gnoll hunting party.