Not so bad for a budget game.
Right at the beginning, you will observe that the graphics date. There is no physics at all. For example, the plants and trees do not move even if it seems to wind. There are very often collision bugs. If you follow a wall, it may happen that the other side or the frame of the wall will be seen.
The sound is poor. The sound level is unequal. Sometimes the characters will talk very quietly and some other times they will talk normally. There are a lot of scripted events that occur through the game and very often, the sound will not be appropriate for the move that your character performed. For example, cutting the throat of an opponent will more sound like if you had broke his neck.
However, there are also strengths to this game. The story is great, there are several items to collect: chests that will give you more clothing, chests that give you special ability for the level, gravestone that explains you the story, etc... However, they are often shiny objects of indicators that give you big clues on where the items are. So, that removes a bit of the fun factor for searching the hidden stuff.
The story is straightforward, you will be on a rail from the start to the end. Some paths will only be unlocked after you did specific actions. However, if you want to unlock everything, you will have to take different paths and them come back to the main point. If you look enough for the hidden stuff, you may miss 5-6 items throughout the game, but not more. That will take you around 12 hours to complete the game, which is pretty decent. However, there is no replay value at all, except at the end where you have a decision to make. If you want to see the different one, you just have to replay the last level and you will be done with the game.
Controls are very easy to get used to. Within 30 minutes, you will master them. The game is also fairly easy, I recommend you to play at the hardest difficulty since at normal, I died maybe 1 or 2 times and it was during the puzzles. Speaking of the them, they are very easy to understand but may be tricky to get through since the collision detection is not so good.
You will gain XP by doing main and secondary objectives which you can then spend in a skill tree for each of the characters that you control. Do not expect something very complicated, but it does it. However, some of the actions that you will unlock will probably never be used by you. I used mostly the same combos and they worked well though the entire game, even in the boss fights.
For sure, you can't compare this to Assassin's Creed, however if you like games that are not complicated, contain action and a good story and you are able to deal with poor graphics and sound, you will be pleased with it. However, if you expect crazy graphics, forget it. The First Templar sure worths a rental for a weekend.