I have experience with the Student Legal Services Criminal Law Project in my time at the U of A. There are multiple projects, one being criminal, one being civil/family, and one being legal education. You can volunteer with multiple so you don't have to pick a lane necessarily.
With respect to the experience, the Criminal Law Project is interesting and more involved than some of the other law schools' criminal clinics. Specifically, many student clinics won't handle Impaired driving files due to their complexity and the charter arguments required in many cases to defend against them, SLS does take a lot of those files on. As a result you're also potentially going to be writing Charter notices for some of these files. These allow you to delve into the more academic side of litigation and help to develop your legal research and writing skills in a practical way. If you're an upper year student (2L/3L) you are able to run trials through SLS which is an invaluable experience. Even if you don't want to be a criminal lawyer, being able to run a trial and live a small part of the litigation experience is fantastic.
Everything SLS' criminal project does is overseen by a local criminal defence law firm so when reviewing disclosure and formulating defences, you're getting face time and are able to draw on the experience and advice of practicing lawyers. These meetings gives you not just legal advice, but practical advice on how to deal with the criminal justice system and the logistics of negotiation/interaction with the Crown's offices. You then take their advice on what the principal should do for resolution or defences at trial, etc, and relay that on to the accused.
Additionally, after 1L you can apply for a day leader position, the criminal law project takes around 12, the civ/fam project takes less than that and for the summer you are a full-time litigator. You make court appearances, negotiate with the Crown, run trials, and work with your principals to help them get the best outcome possible. Day leaders end up taking anywhere between 15-30 files at a time during the summer. You're paid for this position which is nice, and you get a feel for a law office environment.
On the whole, being involved with SLS has honestly given me some of the highest highs and the lowest lows of my law school experience. You're dealing with low income individuals so some of the things they'll tell you are pretty brutal and there can be some tense moments when you are delivering news they don't want to hear. However, being able to assist these communities when no one else will, and potentially help make a significant improvement in their legal outcomes is a pretty great feeling, and a great way to get involved in a community.
As a final note, if you're thinking about practicing criminal law, SLS is ground zero. It is pretty rare to talk to a Crown prosecutor or a defence counsel who went to the U of A and find out they were not pretty involved with SLS in some capacity. The program touches most of the Edmonton legal community and provides a common touchstone for professional connections.
If you want to know more about the law school experience at the U of A, the community, life in the city etc. shoot me a PM, I just wanted to post the SLS review publicly as that seems to be a common request on this site!