I was thinking along the lines of asking if I didn't have a power for it, like at a low level if he would allow me to ask "if I get a critical on this roll, would you allow it to do regular damage but slow him?" type of question. At least that way it's a give and take kind of thing, but I don't know if the DM would allow it. I was curious if this type of thing was common but it doesn't appear to be and seems to be entirely reliant on the DMs style of play. The only thing I can do is ask and see I suppose. Thanks for all the responses though guys, you guys are very helpful and nice.
It's worth asking
If your DM has access to the DDI compendium, or even just AV,AV2, and MME, it's worth looking through them with him, because there's several weapons that have nifty crit effects other than damage.
I love control effects, and find control and action denial a lot more satisfying than dealing damage, so I understand where you're coming from for sure. Be a tad wary of slow, though - it's very easy to overestimate its value as a new player.
Many monsters have ranged attacks, so slowing them doesn't change much. Many maps are small enough that a slowed enemy can still move+charge 4 squares and attack someone. Many of your party members will run up to and engage controlled targets, even if there are other options and even if the target would have had no way to reach a party member to attack if he/she hadn't run up to it.
Situationally, it can be used to great effect, forcing melee creatures to waste a round or two moving towards your party before they can attack, or else to rely on their (generally) inferior ranged attacks. But somewhere around 80-90% of the time it does nothing tactically relevant, unless at least one other party member has World Serpent's Grasp, but even then, proning enemies hurts ranged allies unless they take a feat.
I will jump on the bandwagon of people who have suggested the thief, hunter, and slayer (and why not add the scout as well) as being really excellent introductory classes. They are fantastic classes without being hard to build or hard to play. Their downside is a lack of build flexibility (most of the powers are preselected), but that just makes them easy to use.
The hunter in particular has a large number of at-will options, all of which are situationally useful. Between immobilize, slow, and prone, a hunter can often keep a single melee brute out of the fight until everything else is dead (or until the hunter pings it to death), but once something has entered the fray, Hunter's can't really do that much to stop them.