This is a clean two-star hotel given the lack of AC and the small size of the rooms and tiny TV. There is only one English-speaking channel (BBC world) anyway!
I would NOT stay here in the summer. You will not be able to sleep because it will be too hot and opening the windows means major noise from the grand central station. But it is a good stay for a night or two or anytime it is cold if you want to save money. We had only a one night stay in frankfurt (plenty to see all the good places in frankfurt if you ask me!) and for 69 Euros for two people in April, it was well worth it, especially with the nice breakfast and FREE internet access in the business center, not to mention the location and the easy access to the airport with one train ride of 15 minute duration with S8 or S9.

The Excelsior is right next to the Central train station in Frankfurt, and has tram, underground, trains, buses and a taxi rank on it's doorstep. A fantastic base for travel, you can also walk into town in 10-15 minutes.

The staff were nice and friendly, and the rooms and bathrooms were fine although the decor is a little tired.

There is a free minibar in each room which is great, and there's also tea, coffee, cake and fruit available in the lobby all day. I didn't have a chance to sample breakfast, but it does go on until 11 which is nice.

Pros:
very clean,
reasonably priced,
good location for sightseeing
buffets and restaurants in the main station across the street
minibar (included)
great breakfast (included).

Cons:
no in-room internet; however, available in the business center.

Conclusion
I'll go there every time while in Frankfurt

I booked a guaranteed rate room to save on money in order to be at a hotel right across the street from the hauptbahnoff.

The wireless internet was not working the day I was there and their internet business room was full of travelers using their computers.

The breakfast buffet was OK with a decent selection.

The room was very small and noisy.

The fridge has a free minibar set up.

There were two very small and slow elevators.

The location is near the Romerberg area and with the Hauptbahnof, you can connect to the rest of the city in a short while.