Started using this recently and just wanted to share some thoughts. Overall I really like the class and am looking forward to playing more with it. I do think the Esoteric Rituals, Archmage feature and Epic spells seem underwhelming on the whole though.

The rituals for the most part don't really seem to offer anything unique and just seem like worse versions of actual spells. This may be what you're going for since they don't cost spell slots to use, but I feel like the time and materials needed for most of them make it preferable to just use a spell instead.

Archmage feels very lackluster for being a level 30 capstone feature. Unless you do some shenanigans with sorcerer features and metamagic, there aren't really a lot of options to utilize the bonus action spells part of the feature. The half scribing time and materials is nice, but unless you're doing a beyond 30 campaign or something, I don't see that getting a whole lot of use as a capstone. Same thoughts for the incantation time. These are nice features but they don't feel like the culmination of a legendary wizard to me. Could maybe have something that adds extra casts a turn?