There are one or two small issues with it, though to be fair most of them are already addressed in the e-scrabble FAQ and will apparently be fixed in the next release. It's surprisingly (perhaps because so arbitrarily) frustrating that you can't see how many letters remain in the bag unless it's your turn; and no matter what I do I can't get the word-check function to accept any word, from AT to ZOA, though other people seem to have had no problem. Fortunately, the excellent Collins site offers a free word lookup which not only checks your word for Scrabble acceptability (rendering more or less unnecessary wordlists such as Mattel's list of 2-letter words) but also gives definitions from several dictionaries (including the EIF that is the Texting Dictionary). It's amusing to see how many words are declared "valid for play in Scrabble" yet offer no definition; but nobody thought Scrabble was about meanings, did they? (The words are presumably all in Chambers, famous for its amusing definitions.)
The other main annoyance that many people have noted is the inability to shuffle your letters. It's amazing how much harder this makes it, for me at least; it's almost enough to make me go and learn the l33t w3b sk1llz required to write a separate letter-shuffler. Almost. Of course, you can always cheat with an anagram solver, but that takes all the fun out of it.
In an attempt to keep my brain shuffling letters inbetween games of e-scrabble, I'm also trying to learn to do cryptic crosswords. Chambers help out here again, providing a selection of crosswords to solve online; after a week of extremely intermittent struggling with the most recent one I've managed a pitiful 16 clues. No hints, or there will be cross words indeed!