So I've set about creating some combinations with the words we have so far. Most words created using effects of their level seem pretty comparable to spells of their level, but there's a few interesting effects when using lower-level effect words together in a higher-level word.
But first, a few side notes--
Acid Wave does instantaneous damage and has a sickened effect for 1 round per level, but the duration is listed as 2 rounds, so I believe that is in error.
It isn't clear if spells with two effect words are supposed to be resolved in series or completely simultaneously (this matters for Power Words combined with damage spells, for instance).
Force Ward probably should have an increased cost for making it Mass like the other buff spells in the Body section--as it stands, you can make it Mass without increasing the level, and compared to other 6th-level Mass spells, it seems strong (it guarantees at least +2 to AC, outperforms the top Bracers of Armor as soon as it is available, and lasts long enough to just gather everyone together and prebuff it). Granted, other buffs are generally weaker for the wordcaster, so mainly this is meant to be their "killer app" buff, in which case I guess its fine.
Okay, on to the meat of the experiment!
Word Burning is pretty much crucial for allowing us to create words that cost somewhere in between two levels of spells without wasting points. I'll assume you always burn a word of at least the second highest slot available to leave you this leeway. Let's see what we could do.
Caveat--I know a lot of people think blast magic is weak or worthless, but in my experience, it depends on game style, and we've been given mainly blasting magic, so this analysis will focus on that.
I'll start with a 10th-level Sorcerer:
Fire Blast and Lightning Blast combine nicely into a 15 cost attack that's quite powerful--it does 20d6 damage of varied elemental types, twice as much as Cone of Cold--but it only hits one target. Fortunately, thanks to Word Burning, we can use a single point of burned word points(we have 13 of them per day if we burn a 4th-level slot or 16 a day with a 5th) to spend 17 points and get the Mass target (likely to become a favourite target word due to its precision and its low cost--it would be unlikely at this level to get better mileage out of the more-expensive Small Burst unless your enemies were packed into the burst on purpose). That's pretty darn good damage for a 5th-level spell, and you can do that with all your 5th-level slots and still have burned word points to spare (EDIT: It actually only works with 4th-level slots, using 4 points of the burned word per casting, but on the plus side, that's 4x/day and you only used a 4th-level slot each time, so in a way that's even better). I don't think the normal caster can keep up there.
As I spot more combinations, I'll post them here--please share any such combinations you notice here as well (I think that the combos, rather than just using the flat effects alone, will be where we see the true flexibility of the system and thus where we must be careful when playtesting).
Except you can only apply those Word Burning bonus points to slots 3rd level and below.
You can split these points up among any number of other spell slots, but none of the spell slots can have a level equal to or higher than the expended spell slot.
Which I think still means you can burn a level 5 slot and get 2 of your level 3 slots up to this a day. Or Burn 1 level 5 slot and do this with ALL of your level 4 slots. So yeah, its still a pretty awesome combo, you just can't burn a level 4 slot to power your level 5 slots is all.
Except you can only apply those Word Burning bonus points to slots 3rd level and below.
You can split these points up among any number of other spell slots, but none of the spell slots can have a level equal to or higher than the expended spell slot.Which I think still means you can burn a level 5 slot and get 2 of your level 3 slots up to this a day. Or Burn 1 level 5 slot and do this with ALL of your level 4 slots. So yeah, its still a pretty awesome combo, you just can't burn a level 4 slot to power your level 5 slots is all.
Good catch--I started from the wrong baseline. Yes, the better use would be to burn the 5th-level slot to make every 4th-level spell into "Crimson Lightning".