Essentially, this game takes everything good from Call of Cthulhu and substitutes a coherent system in place of the (to me) utterly terrible old Basic Role Play one. Hite's the perfect author to extract the best of Lovecraft's gameable ideas, too. His take on things is surprisingly fresh (especially his take on the great old ones - each described by a variety of possible explanations, not all of which are consistent).
The system, Robin Laws' GUMSHOE, is all about resource management instead of skill ratings. Investigative abilities will automatically provide characters with the crucial clues to a case (if you have a relevant ability). However, to get extra information you need to spend points. So if you just want to haul ass after the monster, that's free, but if you want to, say, find out how to best kill it, or how it was summoned, those might cost you. I didn't really have very high hopes of this part of the game, but it is actually done rather well. Combined with the advice on mystery construction, it makes a solid basis for playing adventures through.
The other side of the system is a task resolution bit to cover fighting, chases, and other hazards that you will find. You roll a plain old six sided die, aiming to beat a target number of 2-8. In order to boost your chances, you spend points from your ability pool before you roll. It looks like it will play quick and the combat is appropriately dangerous when fighting people and (given their abilities and special powers) absolutely lethal when fighting monsters.
Character generation is pretty good. Like Call of Cthulhu, you pick an occupation that gives you several abilities that are easier to develop. You also get one or two special features based on it, e.g. Doctors can get access to hospital records and so on. You also pick a drive - something that is behind your desire to investigate weirdness. These are a good selection. They have a mechanical affect too - they can be compelled like FATE Aspects, with the reward being increased Stability (more on this below). Finally, you drop a bunch of points on Investigative abilities and another bunch on your general abilities, giving you your point pools to spend on clues and roll bonuses.
The sanity system (perhaps insanity system is more appropriate) is slightly more nuanced than Call of Cthulhu as well. I gather this is because GUMSHOE includes rules for Stability - how well a character bears up in the face of traumatic events - but not for a descent into madness. Hite has essentially mashed them together. Characters are scored for their Stability and Sanity. Stability is used to cope with shocks, and can go up and down rapidly. Sanity goes only down, either when Stability is reduced to 0 by a Mythos encounter, or directly when encountering the most horrifying of creatures. It reads like it will work fine.
The bulk of the book is given over to the descriptions of mythos creatures, general background and advice for play. This is all really good stuff - the creature descriptions stand out, with an effort made to have them not just a list of monsters, but with suggestions to make them more interesting all the way through. The advice on building a campaign is likewise solid, with a lot of good ideas, and suggestions for running the game in many different ways (including totally improvised mysteries). There's also markers throughout the book of rules, concepts and so forth that suit either 'Purist' or 'Pulp' style games. These seem to be well selected, and allow for a continuum of styles from one end to the other, depending on your choices of which to use.
Overall, a very nice Lovecraft game. I look forward to running it - which will happen soon, as I was about to run such a game using Nemesis, but Trail of Cthulhu just beat it for that position.