If you're new to the series, rent this one and start with AC2. The repetitive gameplay overshadows an impressive story.
Pros:
+ Immersive story/cutscenes makes you feel like a true assassin part of a real brotherhood
+ Memorable villains you wish had more face time
+ Altair's evolution from a cold-blooded killer "give me names and I'll give you blood", to a thinking man who begins to question his orders him as the story progress.
+ Well written dialog, incredible voice acting
+ Final assassination stage, end boss encounter and a great ending
Cons:
- Dull, monotone delivery from Altair's voice actor
- Extremely repetitive gameplay can make it a chore to finish the game
- Cheap shots from enemies which can break through your defense
- Combo/Counter kills do not properly execute when you need them the most
- Frustrating informer missions which thankfully can be avoided
- Poor checkpoint system
- No real interaction with other NPC's, no shops, currency, upgrades
- Limited weapons available, sword/dagger are your best bet over hidden blade
- No ability to perform air assassinations
Gameplay / Repetitiveness
Normal abilities automatically given to you in the other 4 games such as grabbing a ledge in mid-air while dropping down from a ledge above, counter kills, and dodge moves are awarded to you for each assassination.
Only problem is, successfully assassinating a target becomes more and more of a repetitive chore the further you progress through the story. Receive names of targets from your master at the fort, walk or ride horseback through the same main kingdom to reach whatever city your target is located while avoiding guards who will attack you if gallop your horse too fast but will simply mark you as suspicious if you run past them.
Every city you enter will be guarded as guards at the entrance will either push you away or gang up on you and attack if you persist too much. To slip past these annoyances, you will have to look for a helpless civilian being attacked by guards and save him / her by attacking and killing off those guards. Once the helpless civilian thanks you, a group of their friends will appear near the city entrance and will allow you to blend in with them so you can slip past the city guards.
Once inside the city, you will have to locate more viewpoints to synchronize the map and reveal the location of the city's assassination bureau leader to find out information and the whereabouts of your intended target. Your contact at the bureau will instruct you to locate points of interest in the city where you can either eavesdrop, pickpocket, interrogate a messenger or someone who works with your target or find an informer and complete a timed, somewhat frustrating 'mini assassination' mission usually 3 or more targets in exchange for more information on your primary assassination target.
After completing any 3 out of 6 combined events of pickpocketing, eavesdropping, interrogations or informer missions, you will be instructed to revisit the bureau leader, relay whatever info you discovered and get their approval to finally eliminate your target.
When you get the green light to finally assassinate your main target, you make your way to the target and bear witness to a pretty entertaining cutscene of your target, publicly performing some evil deed usually on innocent, helpless citizens. Soon as the cutscene ends you must find a way to kill your target. Soon as you kill him, practically every guard in the city will chase you non stop until you break their line of sight and find a place to hide.
When the guards give up searching for you, you make your way back to the city's assassination bureau, exchange a few words with your contact, fast travel back to your master and start assassination #2. Repeat this repetitive process about 7 more times and this pretty much sums up the game.
Story
This is the best feature of the game. Interesting cutscenes and well written dialog explain Desmond's and Altair's (the main chracters) plight very well. It's such a shame Altair's voice actor sounds like he was reading his line straight from a cue card with a dull, monotone delivery. There was great potential for this game, feeling like you are a real assassin, part of true brotherhood, but the repetitive gameplay overshadows everything this game could have been.
All major events that take place in this game are pretty much explained in the beginning of Assassin's Creed 2 which is 100 times better and way more enjoyable than Assassin's Creed 1.
Assassin's Creed 1 is not worth more than $5 or a quick rental if you are really curious to see exactly how the franchise started. Otherwise you are better off skipping this altogether and start off by playing Assassin's Creed 2.