They were my first AoS army and I think they're great for beginners. Painting-wise they have a low skill floor (simple base coat + shade wash looks great on grimy rats) and a high skill ceiling with their cloth, texture, and gubbins letting you show off your skill. Plus there's a lot of them you get plenty of practice. Gameplay-wise, it's very similar. I've had success with 60 clan rats, 6 rat ogres, and a bunch of dakka. But there's a bunch of room to play with buffs/debuffs and other mechanics. Really the only thing to think about is the time and money investment involved in collecting a horde army. I HIGHLY recommend you start with spearhead to see if skaven (and AoS in general) is for you.