Agents are easily the best class and the crypt is not that hard at all, even at level 16-18 or so. The main point is to travel in combat mode, and have plenty of action points. Haste is a minimum requirement for survival, and having a quicksilver plate and boots is ideal. 3 attacks per round means over 300 damage, and with searing orbs, you can blast entire groups of baddies with ease.
The Shaper Crypt can easily be soloed on standard difficulty with an agent. Now, the Inner Crypt is a bit harder. You need 2-3 Ur-Glaaks to take on the boss, thanks to their stun attack. With 3 attacks/round and hasted backup, beating the boss should be possible in 2 rounds. You should easily win as long as your creations don't go rogue.
Here are some general agent tips that show why EVERYTHING is easy to this uber class.
I didn't put ANY points into mechanics as an agent, seriously. Their unlock spell is immensely powerful, and you can eventually buy up the mechanics skill, as well as leadership. If you aren't doing 120+ damage a spell by the end, you did something wrong with your skill points.
Also, Agents don't need any combat skills. They just don't; ignore their "battlemage" starting stats and simply develop them as pure spellcasters. You can get adequate early game melee skills from the Obeyers and Awakened training, and later on, your spells will be strong enough to completely replace melee.
For shaping, the early game fire shaping bonus from Obeyers (THE most important agent faction) is good enough to last you until you get the shaper robe, which will allow learning the other shaping skills at the tombs. By the end, I had a 5/4/4 shaping skills agent without spending a single point in any of them!
All the skills points should be loaded into endurance and spellcasting skills. With high endurance, you can literally walk through a minefield, which, along with unlock, makes the mechanics skill almost pointless to have. Intelligence is also nice, since having cannon-fodder is useful, but it isn't nearly as important as endurance.
Overall, agents are uber before beating the crypts and even more uber after the crypts, to the point where using the geneforge is simply unnecessary overkill.