I played the game on medium difficulty (not really the name, but the level above noob) and found it to be just right. I ran into 3 or 4 sections that were pretty tough but for the most part, the difficulty was just right. I did find that you could kind of cheat in some areas by simply running around a tough adversary, but hey, if I was told to get to a point and I can do it by running like a scared little school girl then more power to me.
Speaking of that - I still run into a few places where I had no idea where to go. But it seemed easier this time then in Halo 3. I'm tempted to just blame myself. I've got a horrible sense of direction and I guess it applies to the virtual world as well.
So - single player is awesome. How about multiplayer? I hate it. I don't just dislike it. I despise it. To be fair, I haven't given it a heck of a lot of time. I've played for maybe two hours. I haven't covered all the modes even. But the experience is just plain frustrating. Let me describe a typical MP game for me in Halo Reach (and this isn't just me - most of the guys I play with regularly would describe it the same) - I'm running down a corridor, come across a badie, and then pump 10+ bullets in him only to have him kill me with one shot. Ok, so maybe I'm using the wrong gun. In a typical game you only chose from one of two or so presets. You can't customize your character. So I go pick up another gun and get the same result. In fact, out of all the kills I've gotten in Reach (which isn't much), 90% of them were from melee attacks. I'm sorry - but I thought I was playing a first person shooter?? I've heard others say I should just go for head shots. Well, I get that a head shot will always be better. Fine. I'm not that good of a shot in COD either, and I can still get by well.
As for game advancement - again it feels much shallower than COD. Gaining levels seems much slower. I gained maybe 2 levels over the couple of hours I played. From what I can see I'd probably need 3-4 more hours to finish the level I'm on now. However, from what I can see advancing gets you absolutely nothing at all. You can buy armor, but it's all cosmetic. Woot. I can't wait to spend 10 hours so I can buy new shoulder pads that add absolutely nothing to game. Yeah. To be clear, I don't mind cosmetic changes - they can be kind of cool - but if that's the only thing you gain why should I bother?
Reach's MP isn't all bad. It is much easier for your friends to join your party compared to COD. In COD you have to invite people, and I can't tell you how many times I'll invite friend A at the same time he invites me. Then you have an awkward situation of wondering if you should accept his invite or wait for him to take yours. Reach just plain works. Also - I like the idea of the Firefight mode. I think I tried it once (I'll be honest - I think I played it once a bit inebriated) and the idea is cool - basically see how long you and your friends can survive against waves of enemies.
So do I recommend Reach? Absolutely. I've got multiple games where I enjoyed the SP and never even bothered with the MP. (I'm playing Transformers now too and will write up my thoughts when done - but to be honest I don't see bothering with the MP.) If you enjoyed Halo at all, I think this is easily the best game in the series for SP. While I hate the MP, and some of my friends agree, not all of them. So that being said, I'd definitely recommend picking it up.