Noisy and isolated
There seem to be two parts to the Waterloo Inn - the hotel and the conference center. Our room was in the conference wing, which we found to be noisy, crowded and isolated from the hotel services. On one night, people at a late celebration in the conference center kept wandering past our (2nd floor) room talking and laughing loudly until about 2:00am. The conference center is on the back of the hotel, and it's a long walk to the lobby, Rushes restaurant and the bar. It appears that the hotel wing has rooms surrounding the pool, with nice patio areas, and I suspect that those might be quieter - they're certainly closer to the services.
We had trouble with housekeeping, as our room was never cleaned when we would return to the hotel at 5:00pm. We had to wait until nearly dinner time for the room to be serviced on all three days that we stayed.
As for services, there is a small fitness center and a very nice pool. Breakfast at Rushes is just okay and very expensive, but there are some nice cafes down King St where you can get a reasonable breakfast. The wireless internet is fast and free. While there is a Via Rail train station in town, there is no direct public transportation to the hotel (that we could find). You'll need a car, or at least a taxi from the train station.
Overall, I'll look for other options when staying in Waterloo again.