First of all, this is PVP retro, not overall retro. They are specifically going back to certain PVP mechanisms from the past. Not the game. PVP.
So, please, before complaining about anything content-wise, read the entire news.
Although, if it were overall retro, there are still people with mixed opinions on this.
Content-wise (areas, quests, monsters, outfits, mounts, items, spells, etc.), 10.51+ is the best at the moment. Although, some exceptions may be considered (magic shop NPCs selling runes).
Honestly, if you try to actually play Tibia (don't focus on PVP) in 7.4 or 7.6, you will cut wrists, it's so suicidally boring, it's not funny.
Even if you find some fun in it, you will be craving for new content after half year, year or so, I can promise you that. So, content-wise? Don't touch it.
Technical-wise, yes, there are some areas where they should go back to what they had in the past.
Most of them are anti-cheat measures though, like aimbot, ambient light, soul points, stamina, etc. Some should stay (stamina), some should be removed (ambient light).
Aimbot is probably needed still, although, can be tweaked. Allow the ability to execute action hotkeys (items, runes) on monsters, but not on other players.
What this means is we can use aimbot to hunt, but have to actually use aiming skills in PVP. Why do we still need it? Good luck doing quests (any major ones) and hunts (Zao/Roshamuul) without it.
Cooldowns should stay, every MMO has cooldowns. Collectively spamming the most powerful spells in the game every 2 seconds is definitely a problem.
This is just some of the things to talk about. Be appreciative of what CipSoft is doing, this is partially what we have been begging for (strictly talking about PVP).