Syndicate is absolutely good. I finished Unity a couple weeks ago and immediately started Syndicate upon finishing. Combat is a lot better and has a lot more options now. The multi-kills are all pretty cool. There are a lot less weapon types than Unity, which I consider a positive. I assume that is because the vastly different kill animations with the three core melee weapons in Syndicate, they wouldn't have had time to do that kind of work for all of the different weapon types in Unity (and I just stuck with regular swords in Unity, there was too many options for me to settle on something else). They game looks great on the Xbone and I haven't seen any bugs. So yeah, I would suggest picking up Syndicate. I recorded a kill that I pulled off in the very beginning of the game with Evie, the kill animation was absolutely brutal and completely over-the-top overkill. I thought it was completely badass and showed it to a coworker who has not played a single AssCreed game and thought the series was not worth playing. That and some of the recorded footage of combat in the boxing matches have possibly sold him on the game though. He was watching the combat in the boxing matches and said "This seems a lot deeper than 'press counter' to win."
I have actually loved all of the AC games I have played, minus 3. My problem sometimes though is if I am coming off another Creed game or another UbiSoft open world game, the Ubi formula fatigues me and I have to take a break. I played AC1, 2, and Brotherhood back-to-back and loved all three of them. I started Revelations right after Brotherhood but I just wasn't feeling it so I shelved it. After a year or so I returned to it and had a blast. After that I started 3 because it had just released and I hated it. I gave it some time and tried it again but have yet to finish 3 and don't imagine I ever will (I might give one more another try if it becomes backwards-compatible). I started playing Black Flag last year and I think it is the one I enjoyed most, probably due to it being a fantastic pirate game if not a great Assassin game (some of those tailing missions were horrible). After Black Flag I started Unity and Watch_Dogs. I liked Watch_Dogs better and could not patch Unity at the time, so Unity got shelved. After returning to the US and having access to unlimited internet in the fall, I was able to patch up Unity, so I started that again. Unity was good and I liked the story up to the end, but locking good gear and upgrades behind co-op missions that have to be played multiple times each if you play solo rubbed me the wrong way. Upon beating Unity, I started up Syndicate and am on the 6th set of missions right now.
Altogether I have enjoyed the series though. I've beaten six of the eight games I have played so far and have 100% completed/synced (all chests) more than a couple, will have Syndicate beat soon, may return to 3 one day, and will play my sealed copy of Rogue as soon as it becomes Xbone backwards compatible.