I have covered a lot about the different spell casters and fighters so here is something about rolemaster thieves.
We have a sliding scale with the more violent at one end and then less violent the other. On that scale then the thieving classes pretty much fall into the order that I listed them in the title. The rogue is almost a cross over between fighter and thief, they get the best (cheapest) weapon skill costs at the expense of some of the subterfuge skills. They can still learn them but they are a little more expensive.
The thief is also called the scout and is the best all round adventuring thief with passable combat skills albeit with a limited range of weapons, good subterfuge skills and the outdoor skills to rival a ranger. Your burglar goes the other way with the best subterfuge skills but weaker in combat. Where the burgular really excels is in acts of concentration and at climbing. The official dummary of a burglar reads “He is similar to the normal thief except he has avoided almost entirely the awkward encumbrance of armor, and instead dodges and ducks very much like a martial artist.”
The final member of this team is the Nightblade. The nightblade has worse weapon and armour costs than the straight thief but has similar subterfuge skills. The big advantage is that the nightblade is a semi spell caster. As a mentalist a nightblade can wear any armour as long as he/she does not wear a head covering such as a helm but given the points cost it is going to be a bit of a hard slog to learn armour.
I have never played a nightblade so all this is theoretical. With semi spell users generally what works best is to avoid buying any magic or invest a minimal amount of development points into magic and just let it ride for the first five levels. At about fifth level something happens and that is that your core skills that you have been developing start to hit the first point of deminishing returns. Secondly some skills are ‘finished’ by that I mean some skills like armour only needs to be learned to a particular point and after that no further bonus is gained. So if you have been learning armour then you no longer need to spend points on that so you can put them into spell lists, if you were buying two ranks in your weapon skills (12 points) to gain +10 per level that would drop to just +4. If you go to just a single rank per level it costs 3 points and gives a +2. I would settle for the +2 to my attack roll and put the other 9 points towards my spell lists. The core thiefy skills are going to cost so something like 2 points for a +2, 7 points for a +4, so take the +2 and put the other 5 points towards your spells. You get the idea I hope. Everything you need to do still imporves but you can probably find 20 or so points every level to build up your spells. Also by fifth level you should have enough power points to make use of the spells as you gain them and you may well have found a spell bonus item (that allow more spells to be cast each day) to further boost your magic. Finally by starting to learn spells when you are 5th level means that when you do learn a list at least you get a handful of spells for your effort. Learn a list at 1st level and you get one spell and barely have enough powerpoints to make any use of it. Finally if you wait until you are about 5th level to learn magic your fellow adventurers may not even realise that you are a spell user at all and it is something you can keep under your hat.
A final word on the nightblades magic. This goes for any semi spell user really but you do not have to learn all your base lists (those special to the nightblade profession) it is entirely viable to learn the open mentalism lists as these are often better than the nightblade ones. There is a nightblade list relating to poisons. If you GM doesn’t want you using poisons any way and gets fed up with you killing everything that way then buying magic to amplify that is not going to go down well. On the other hand buying the mentalist healing list is brilliant for an adventurer, being able to see into the future is useful as being able to detect magic items. There is more to nightblade magic than the nightblade base lists.
There is one thing that makes all thieves stand out and that is that they are probably the single most useful professions in all of Rolemaster. Their skills extend into combat, stealth, subtly, information gathering and even magic and healing. A well rounded thief is almost never out of options and is always an asset to his team and can slip into any role. Th eweakest thief is probably the burglar and that is only because he has chosen to move away from that ‘all rounder’ characteristic and becomes a little bit more of a specialist.
Others of course may disagree.