Ok, first thing - that "recommend" is more like "take it at your own risk". Shame there is no such option. With that said - game is not exactly bad, but it has a lot of flaws. But let's start with good part - game has lots of maps (35+), lots of modes and difficulties and nice interest system where you have to keep your defences to minimal, which adds to tactical part. That's about it for the good part.
Now about bad stuff - first of all, game is really
long. Each stage (except maybe very early ones) lasts at least an hour. On it's own that wouldn't be so bad, but you can't speed up the game more than 2x. Considering that some games has 3x, 5x, even 9x speed ups - very poor desicion. Next thing - in every stage to collect more money (and gain more interest money) you have to do your best to kill enemies withlou building anything. So you have to use abilities and your commander (yup, you have movable unit to help you) for a good 20-30% of the stage. Way to go for a TD, instead of tactical managing limited resourses you must jump around to collect money. Another bad thing is - there are basically only 8 types of enemies with small variations, nothing interesting really. If that was a game for 20-30 hours, it'd be ok, but game for 100h+? Definitely bad. And there is more! Towers are majorly disbalanced, by the end of the game you really need only 4-5 towers from given 12 - as if 12 was too much to make it more or less balanced. Well, that's it for big ones, i may also add couple small ones - bad graphics (but i guess if you play TD you don't care like me, still had to write about it), repetitive music (remember 100h+ of gameplay, on the other hand you can turn it down - again, like i did) and small glitch when you choose chapters, but that's not really an issue, just a bit annoying.
So. After all that you may ask why i even put "recommend" on it. Well, not everyone completes games on 100%. If you want to complete campaign and leave, i suppose, it's not so bad. I give this game 5/10, because it's badly flawed and artificially prolonged, but you may still enjoy it. Just don't go too deep.