Foxton is my favorite run. from 240-300cfs the water is very low and lots of rocks. still runnable, but don't bother if the flow is lower than 240. the best water level is 350-500 I think. I haven't run it higher than that. I hear some of the bigger drops become class 4 when the water is at 600cfs or higher.
there are several sections- the boulder garden is the highest section and also the most difficult. don't bother unless the river is at least at 350cfs. This section has big boulders and lots of maneuvering. I'd call it class 3+. It's a lot of fun but definitely more technical. At higher water levels it may be a class 4. This section includes the 2 big drops mentioned in the previous post.
The next section- below the boulder garden to just above foxton road is class 2/3. pretty mellow with 3 or 4 easy class 3ish rapids near the end of this section.
Just above foxton road starts my favorite section of foxton. there is a huge boulder on the road side of the river, put in above there. Lots of play, continuous rapids for several miles. 2 largish drops about 3/4 of the way down. Lots of maneuvering and some holes that are fairly easy to punch through at low water but can be sticky at high water. This section ends at the big parking lot a bit downstream from the short narrow canyon-like section of the river, below the big drops. At high water some of these drops become class 3+, and at 600cfs or so some will probably be class 4.
The next section is down to the confluence. It's fairly mellow most of the way but has a few decent sized class 3 rapids and some maneuvering.
If you put all of this together it's a solid full day run
Tons of fun, and all can be scouted from the road. A detailed description can be found at http://www.coloradokayakers.com/viewtopic.php?t=28
hope this helps!!