Protector tries to be a RPG and Tower Defense Game rolled into one. While it doesn't really succed at being an RPG, it has enough elements to make it a very good TD.Place your units throughout the board to stop the oncoming hordes. Let too many get by you and it's lights out. Place your units wisely and you can win any board. Place them poorly and you're sure to lose.
There are five basic units red (splash damage), blue (slow), green (poison), purple (electrocute: debuff), and dexer (high damage land based attach). There are four more advanced units: alchemist (splash damage, land only), archer (high damage against flyers, but not land), necromancer (high damage, but based on number of kills) and paladin (high damage land attack).
Your units earn XP based on how many times they attack and do damage to an enemy. You can't level a unit up unless he has enough experience, adding a new twist onto the level up/money equation. Because of that, it may be a good idea to build up the back of your maze first, then start building up the front. Otherwise the units in front will get all the xp and the ones in back will be very inexperienced in the later rounds.
There are two basic types of enemies: flyers and land based. Keep in mind that dexers and paladins cannot hit flyers.
Basic strategy involves a lot of red mages, with a green mage and/or a blue mage near the entrance. Keep in mind that effects are not cumlutative, so it's not worth stacking a bunch of blue mages. Also, don't put a lower level green in front of a higher level one, because if an enemy unit is still being affected by the lower level mage, it won't take on the higher level mage's effects.
When leveling your units up, you can choose to level up their special attack (recommended at least first two or three levels, otherwise you don't have the special attack) or the general expertise (much stronger basic attack).
Once you beat a map, you can get skills such as lower cost of units, more damage, faster learning (more xp), etc... You can always reset the skills you have chosen, which means you can try building up a superarmy of red mages, then try a more moderate 'spread the skills around' strategy without any penalty. Your skills also unlock the more advanced units.
All in all, this is a pretty good TD game. It can be slow at times, but with many maps (I haven't worked my way through all of them, yet), you should be able to find a map you find challenging. It is probably worth working your way through the easier maps (medium level) first, allowing you to build up your skills for the harder maps.
Play Protector at Kongregate.
Update: It seems a lot of people are landing here looking for a FAQ, walkthrough, or some details on the more advanced units. If you have a question, leave a comment. I'll try my best to answer it.
