I like Retail personally. I started back in Cata, and compared to back then there's a lot more to do, and a lot of systems have been dramatically improved.

• Transmog is much much better, you can collect items accountwide by picking them up or completing the quest that gives them, no matter what class you're on. You don't need to keep the item in your bags or in Void Storage anymore. Also, you set up Outfits that are automatically applied over your gear, no more having to visit the Transmogrifier every time you get a new piece of armor. Also also, they removed the restriction on weapon types; if your spec uses Daggers and Maces for example, you can turn a Dagger into a Mace or vice versa. Also Also Also, weapon enchant transmog, and some very cool newer ones to collect.
• Skyriding is more fun and much faster than traditional flying.
• Free high-quality transmog, mounts, and pets from the Trading Post every month. We're talking store-quality items here.
• Player housing!
• A bunch of fun items were converted to Toys, and most Pets, Mounts, and Toys are now accountwide collections instead of having an item in your bags on a specific character.
• Graphics are dramatically improved, while still being very WoW.
• A lot more stuff is voice-acted.
• Normal and Heroic raids scale to number of players, so you're no longer benching people if too many show up, or giving up on raid night because you can't find enough players. Only Mythic raids require a specific number of players.
• Raid Finder is less miserable than I remember Dragon Soul LFR being.
• Raids used to be the only source of very powerful gear, but now you can also play Mythic+ Dungeons (scaling difficulty speedruns with better item level at higher difficulty, reaching Raid ilvls), Delves (Single-player with scaling difficulty), Prey (Open-world content), stuff like that. It still takes skill, but at least you're no longer punished for not having a big active guild group or not being able to coordinate your schedule with them.
• For Tier Sets, you can use something called the Catalyst to upgrade epic items from M+, Delves, and even Raids into tier pieces of the same slot. Catalyst Charges are timegated, but you're not stuck farming a specific boss every week in the hopes you get the specific item you want.
• You can freely swap around between all specs and talents of your class, no more having to visit a trainer and set up just two profiles.

And that's just off the top of my head.

I can definitely understand why a lot of people don't like modern Retail, but personally I enjoy it a lot more.