As soon as someone moves this to fanfiction it won't be in the wrong topic anymore.
Since you asked (
), here are my thoughts which pretty much reflect the above post that almost ninja'd me:
The Samurai Dojo is pretty OP, and you were right about how it doesn't solve the problem of barracks being really similar. The chain strike is cool, but I don't know if it's an ability or a passive, the latter being extremely OP and the former requiring a long cooldown to comensate. The other skills are passive stat bonuses, which is lame. Why make a tower if it's just a bunch of statistical upgrades? Have abilities that contribute to a theme and playstyle which ultimately achieve the same goal of either making the tower more durable or offensively effective, but not through boring number buffs. Durax is strong but he doesn't become that way because he has an ability slot that increases his stats and ability power by 50/100/150%, he has a power that clones himself to create a playstyle around that idea, achieving the same effect but in a much funner way. Also, why are Samurai resistant to magic? Vez'nan isn't resistant to magic, the Forest Keepers and Holy Order aren't, Nivus, Magnus, Elora, and Arivan aren't, and to broaden the scope, not a single allied unit in the game is resistant to magic even when they fit the role better than some Japanese warriors.
The Dragoons are the same way as the Samurai, with nothing but stat boosts. The lance attack seems nice, but the lack of detail regarding how exactly the ability works makes balance and purpose questionable. Also, just like with magic resistance, what have these units done to warrant getting 4 of them instead of the usual 3?
The pirates are a bit cooler, even if they rip off the Assassins, at least they're stealing from arguably the most fun barrack in the game. They also steal Circle of Life/Dwarfwheiser, but the stun ability is something interesting as it adds to their blocking ability very well. I still think it needs a lot of improvement regarding detail, balance, and originality, but it's a step up from the previois towers.
The Moon Druid is a cool tower, and as ridiculously OP as it is, I like the unit-summoning skill and stun, which all contribute to keeping enemies at bay in groups, making it very supportive and good against the specific threat of fast, armored enemies, which doesn't exist as of now, but would be cool in the future. Best tower so far.
The Warlock has a pretty good setup as well, slowing down enemies so he can group them together and destroy everyone in a big explosion of fire. As simple as it is, it would definitely be really fun. Not as much detail as I'd like, but that's for all of the towers so I won't drive the point any further than necessary.
The Voodoo Master is also a great tower, though I wish you would've gone further with the idea of the Pins and Needles. It seems like a stronger version of the Wild Magus's awesome passive, so something that adds more but retains balance would have been much more appreciated.
How are archers not good in later levels? Their focus is to support the rest of your towers, so building them alongside others is a very effective strategy in a majority of KR and Frontiers levels. Origins shrekt the idea by making mages and archers better than artillery at DPS and crowd control, which isn't good but at least it means that archers are really powerful. I can sum up every archer tower with this: The ideas are pretty good, but they lack a central playstyle like the mages had and they're all very, very overpowered.
The Oiler Boiler is pretty cool, though it's hard to tell if it's balanced without skill cooldown times. I like the powers, but why does the oil deal magic damage?
The Blacksteel Bomber is the Big Bertha but with OP stats and very OP upgrades. I like the 2nd skill, though, if not for the fact that there's another artillery with an instakill, which again doesn't mix well with the other towers.
The Plasma tower is OP, but it reminds me of the Contained Magus in the contest since it focuses on dealing with groups of armored enemies more effectively than regular artillery, but is less useful against magic foes, making the player decide between equal effeciency over all enemies and imbalanced power toward both types of resistances to create an overall balance. That's great, but it's not balanced because of the OP upgrades and stats, killing the whole purpose of the tower.
You've got potential that will get to a point where it's super awesome, so I wouldn't stop trying to make towers just based off of my opinions on the towers, as this is your first attempt, and I think everyone falls under the category of having lackluster first attempts at FanFiction stuff.