I've just completed the GOG anthology of the game and I wish to write my thoughts.
This is an episodic game consisting of six chapters each spanning for 4-9 hours. There are options to start a mage, fighter or scout (aka archer), I sticked to mage and it was the right decision, because playing as a mage was irritating enough, but I am not sure if it is possible to beat the game with pure fighter. Experts say it is impossible, but maybe someone knows better.
Nevertheless you free to train any attributes or skills, so you can play as spellsword or any other crazy build you can end with. You definitely need magic as I say, but otherwise, you can use armor, weapon and other stuff according to your style of play. Character advancement is fine, scaling through the game is significant. Combat on the other hand is a bad copy from Diablo - it is tedious, boring and full of trash mobs. See also description of later chapters below.
The story is somewhat intriguing and good overall at the beginning but loses some grip near the end. There are a lot of texts, logs, dialogs and books, and the writing quality is very adequate for a CRPG.
Speaking of Chapters here are my thoughts:
1. The best chapter. Starting a bit slow, with the possibility to catch the nasty bug in one sidequest, but decent and intriguing.
2. Here comes a lot of backtracking and trash combat. The story is still good, but combat becomes much worse if you take companions into your party. Any fight with allies turns into a circus with running in circles, friendly fire (remember Ian from Fallout1? In this game your archer companion will shoot your ass every other fight) and random deaths of your allies because of stupid AI. Better not take them.
3. This and the next two are optional, but I do not advise you to skip them, maybe except the fifth. The amount of backtracking increases, but this chapter is pretty good as soon as you withstand trash encounters everywhere.
4. Here comes the tedium. The idea of this chapter is interesting - infiltrating the enemy camp and stealing, killing and looting everything your can. But in practice game introduces here endless spawns of enemies and invulnerable enemies. These instruments used here to enforce a stealth approach but it looks unnatural as hell because your hero already so strong that can kill dozens of enemies in a second.
5. Clusterfuck chapter. The game introduces mage enemies and mage duels in the game are about who is the first to cast Hold on its enemy. If you faster - you kill an enemy while it is paralyzed. If he is faster - you load the game. It turns tedious combat into random tedious irritating combat. Good luck in surviving this chapter.
6. Clusterfuck chapter 2. Here comes the end and all bad elements come together with the final boss being A Big Bad Mage. In theory, the story comes to conclusion organically, with a bit of drama and should be satisfying but in practice chapter writing performed pretty average and uninspiring.
In general, Siege of Avalon is not a bad game. It is mediocre with the good story and atmosphere in its first half and bad combat and a lot of tedium in its second half.