Here's a rundown on the Far Realm (which I jumped to because I'd never heard of it

)
In summary, based on the fluff, it is definitely Lovecraftian but more on the 'outside and bizarre reality' side than the 'outer space' side.
The Far Realm is formally acknowledged in the cosmology, and 'is responsible for monstrosities that haunt the universe'. Specifcally, all aberrations are linked to it.
A Far Realm specific reason is suggested as a source of the conflict between the illithid and aboleth.
Perhaps taking a cue from WFRP, the Far Realm is said to 'seep in' sometimes, overlaying the landscape with an unnerving sense of dread, even distorting it, and tainting the flora and fauna. Strange new creatures emerge from this 'polluted reality' and insane practitioners sometimes 'willfully merge the natural and the obscene'
Also mentioned is that aberration is not a type. Type is now distinct from Origin - so you have Humanoids (type) with an Origin of fey (eladrin) , aberration (mind flayer), elemental (archon) , natural (man)
Finally there's a page and a half or so on the mind flayer: in short: they are essentially the same as in the previous edition just with fewer powers (taken from the set of those that most define them) that are easier and clearer to run. There are a few mechanical tidbits about mind blast and dominate each being a 'renewable power - useable once per encounter', whereas tentacle lash and grab are basic attacks backed up by situational powers 'bore into brain', 'thrall' and 'interpose thrall'
So far the book seems to be pretty close to Races and Classes in terms of value - and for me it is having the same effect: reinforcing my faith in the designers, making some things clearer in a positive way, increasing my enthusiasm for 4e. If you enjoyed R&C I'd recommend it.