Fly fishing reels are what allow you to bring in that trophy that you’ve worked so skillfully to hook. They complete the rod/reel setup and therefore can be a weak link in your gear. On the other hand, if your rod is mid-quality and you have a top-of-the-line fly fishing reel, you probably would have been better off investing in a cheaper reel and a better rod. Much like rods, there are people way more qualified than me to talk about the specifics or different drag systems, arbor types, etc. I only intend to give you the perspective of someone that’s been through the initial startup phase and tell you things I’ve learned or wished I knew.
I must admit that after 1 year of fly fishing, I don’t know much about the inner-workings of fly fishing reels, and don’t think a beginner needs to be bothered with them either. However, there are a couple basic things to know about fly fishing reels. First, they are made of different materials, and the material contributes to the overall price. The second price point is whether the reel is cast (formed from a mold) or machined (out of a since piece of metal). Machined reels (I’ve read) are more durable and are therefore more expensive. The third thing to be aware of is the drag system. Most reels that I’ve seen and read about are disc drag systems and are what I use on my rods. Unless fishing for very large fish, any drag system will work fine starting off. Like the rod, My suggestion would be to get a reel that is middle of the road for your first setup. I’ve purchased fly fishing reels for $30 that have not failed me yet (although I haven’t put them to serious use yet), so don’t feel like you have to spend $100 upfront.
Whatever reel you decide; make sure you match it to the rod weight. Fly fishing reels are a bit different in that they are often compatible with 2 different weights (e.g. 3/4 wt or 5/6 wt). The ability to buy a second spool stretches your money even further, because you can have 2 different types of line ready to throw, or 2 spools of the same line once one gets water-logged. The only downside is if something happens to the actual reel, neither spool is usable. I have a 5/6wt reel with a weight forward line on it and an extra spool with a double taper line for smaller streams from Albright Fly Fishing and a Cabela’s Wind River 4wt reel (WR1). For a more in-depth comparison and explanation of fly reels, check out this article from Hook & Hackle.