So I tried the beginning of BG2 with a Wild Mage and it went approximately as I expected : I paralyzed myself, I turned myself into a wolf twice (how do you even undo that ??), I fireballed my entire party...
It is certainly a different experience, but I'm not sure I have enough chaos in me to play the entire game like that.
Some tips for Wild Mage:
- I prefer a solo mage as it helps negate some of the more nasty surges.
- Avoid using the NRD for buffing as roughly (IIRC) half of the bad surges are target based.
- Always have at least the basic Chaos Shield up before casting NRD. If you wanted you could cast a Chaos Shield before any buffing coming from your Wild Mage.
- Never cast typically harmless spells around civilians.
- Always have some way of giving your party protection from evil handy in the rare event a demon is summoned.
I did some math looking at the effects of wild surges. Assuming you are just rolling a D100:
53% of bad failure (replacing the spell or harming you)
32% chance of neutral failure (visual effects, almost never harmful)
6% chance of re-targeting or re-rolling effect
9% chance of spell casting successfully (usually with some modifier)
If you're level seven, it looks more like this:
51% of bad failure
27% chance of neutral failure
6% chance of re-targeting or re-rolling effect
16% chance of spell casting successfully
Chaos Shield and Improved Chaos Shield add 15+ and +25 respectively. A level 7 Wild Mage with Chaos Shield active looks like this:
(Note that All the party's gold is destroyed effect is removed and only the target based roll is left)
39% of bad failure
24% chance of neutral failure
6% chance of re-targeting or re-rolling effect
31% chance of spell casting successfully
Already things are looking much better for the wild mage. Lets look at level 14 with Improved Chaos Shield:
33% of bad failure
16% chance of neutral failure
4% chance of re-targeting or re-rolling effect
46% chance of spell casting successfully
We're now at the point where you have almost a 50% chance of your NRD working. For a solo player this is basically some misc quests within the city.
At level 31 with Improved Chaos Shield it looks like this:
26% of bad failure
10% chance of neutral failure
2% chance of re-targeting or re-rolling effect
62% chance of spell casting successfully
If you aren't adverse to abusing the game, level 18 with Chain Contingency and triple Improved Chaos shield will push your chances to 97% chance of success. Level 23 puts it at 100%. Some mods will remove this "exploit" however.
EDIT: Keep in mind that everything I just spoke about is strictly in regards to Nahal's Reckless Dweomer: you are otherwise a specialist mage with no spell school restrictions with a D20 roll on spells casts to check for a Wild Surge.
Note that the chances for a level 7 mage to have a regular spell end in any failure is 3.8%.
(but the most cheesy fight in BG2 that I can recall was the final battle from the Solaufein mod)
(I've screwed up the dialogues before, ah well, seemed a fitting end) 
