Hard to say, since everyone above me put in very excellent likes and dislikes!
Likes:
An adult series, both in theme and actors! I prefer my rangers for the most part to at least appear as if they have passed through their Coming Of Age day when they turn 20 and are legal adults. Of course one can have the exceptions like Boy in Zyuranger, the entire Megaranger [still in high school], or Hikaru in Gingaman.
Foot soldiers who can do more than merely fight and get killed off on cue. Like drive the Suzuki Samurai jeep or its modern equivalent, do tasks like mix the evil lab formula that a general will then take credit for, and have speaking lines. And perhaps survive to the next battle.
Actors who look like they can do their own stunts. I know in the early days the lead actors were often members of the JAC and a few were in-suit as well as being the face. While it would be a shot in the arm for Toei to do a modern series with JAC/JAE members as the face actors, until the producers get out of their current creative box it'll likely never happen again.
Dogs. For some reason, whenever there's a dog in a super sentai or toku, it's always cool; especially if they have speaking lines. Denzi Dog. Doggie Kruger. The skateboarding dog in Liveman. Springer from Metalder.
Dislikes:
Well... the opposites of the above! Kids in Super Sentai are a time honored tradition, and I sometimes wonder if any of the kids in these shows ever grow up to become actors in toku. But there is a place for kids in any super sentai, and it's not to be the team leader or Red Ranger. Ever.
[except if the story calls for it...]
Lame foot soldiers. While I don't remember ever seeing super sentai grunts be as lame as MMPR Putties who show up just to warm up the rangers before the real fight against the monster, armies who show up just to get their asses kicked gets pretty dull after a while without them doing something a little different to relieve the monotony, like the occasional motorcycle stunt in the Toei quarry.
Actors who have "Kick Me" signs on their backs. The entire cast of Goseiger comes to mind.
Cats.
[just kidding -- I like cats... but after seeing Goseiger I just might have to check out Gekiranger which I originally despised!]