Probably the best collection of new 3.5 spells from a third-party publisher that I've seen -- and believe me, I've seen a lot of them!
Sure, there are a few spells which seem too vulnerable to player-abuse, or which make you say, "What were the designers thinking?", but this can be said of any collection of spells, including the ones in the Dungeons and Dragons core rulebooks themselves. In recommending Eldritch Sorcery, I'm presuming that the buyer will review the spells he or she decides to add to their game, and that the DM will actually think beforehand about what using a given spell might mean.
What makes this all okay, in my opinion, is that Eldritch Sorcery contains a LOT of spells, so even if you have to discard a few in the name of home-game balance, you'll still have plenty of new spells left to put into play.
Particularly, this isn't an "uber" book -- meaning that, while there are some pretty powerful spell ideas herein, it's not just another "munchkin book" designed to give power-gamers orgasms.
What I especially like about Eldritch Sorcery is that it tends to fill in a lot of spell list "concept gaps" for me.
If you've every found yourself wondering, "Why isn't there a spell at this level which does X", you might very well find that spell here, in Eldritch Sorcery.
There are more than a few possible "D'oh!" headslap moments, where you could find yourself reading a spell description and thinking, "Well, of course that character class should have that kind of spell at this level!"
For example, druid characters get a lot of interesting low- and mid-level spells offered, which suddenly make the class a lot more versatile, well-rounded, interesting, and fun. I can honestly say that this book made me think about actually playing a druid character for the first time in decades of D&D gaming.
Also, there are a lot of new Evil and Necromantic spells here (as befits a Necromancer Games product, I suppose), which will allow DMs to have their evil villains hit the players with suitably nasty and spooky magic whic players haven't already seen a hundred times before.
A villain who can surprise the players, and make them sweat a bit, is always a better villain.
Most spell-using character classes in D&D get new spell options in Eldritch Sorcery. Prestige Classes like the Blackguard may only get a handful, comparitively, but that may be simply because the core classes get quite a lot. There are new clerical domains provided as well -- all of them are interesting, if slightly obvious. Only the new Necromantic domain truly wowed me with its game-potential.
WHAT'S NOT SO GOOD?
As I said in the introduction, Eldritch Sorcery has got a few spells among the many which seem unbalanced, or else just "wrong" somehow. That's to be expected, especially with a spell list this large. This all means that DMs will have to review each spell, and think about its impact, before allowing it in their games. Good DMs do this with third-party game products anyway, but it does work against the pipe-dream of an absolutely plug-and-play spell compendium.
WHY 5 STARS?
While not perfect in every last respect, Eldritch Sorcery makes an obvious and sincere effort to give over-worked DMs more options toward better, more fun, gameplay. Also, the sheer number of new spells in this book should mean that every buyer can get his or her money's worth in some way.
As I mentioned, I've seen a LOT of third-party D&D spellbooks over the years. This is definitely one of the best. Recommended.