I stayed at the Holiday Inn Hannover Airport for 2 weeks in October 2011. The hotel is about 10 minutes walk from the Hannover-Langenhagen airport and offers a free shuttle service from and to the airport. I booked a business package rate that includes breakfast, internet access, and parking. Else, everything would be charged a la carte. The only thing about the business package rate was that the internet access included in the rate was not unlimited and does not have a premium business access. That translated to a slower wi-fi connection and occasional hiccups when browsing the internet or opening emails with attachment files.

One major plus about this hotel is that considering its close proximity to the airport, I could hear neither airport traffics nor outside noises from inside the room. Additionally, for an airport hotel, the onsite restaurant has a pretty decent dinner menu. The selections are good enough for business travelers who want to have a quick dinner without having to search for local restaurants. A side note for American travelers, many local restaurants do not accept US issued credit cards. There is a pretty good local restaurant (about 10 minutes drive) called the Baumhaus. It takes credit cards and serves authentic German food.

This hotel is at least 25 minutes drive from Hannover City Center. However, there is a suburban train (S-Bahn) from Airport Terminal C that runs every 30 minutes between the airport to the Central Station. It takes approximately 20 minutes ride; and a one way ticket costs EUR 2.80 (or the unlimited daily pass for about 5 Euros and some change).

Another major plus about this hotel is the service. The restaurant wait staffs were great; but the extra kudos go to Saskia, the Front Desk Manager. She is very professional and knowledgeable about the surrounding areas.

In summary, it is a decent airport hotel with great services and a 20 minutes train ride away from downtown Hannover.

Stayed here often, when my flights would leave early from Hanover airport.
They just remodelled the lobby and it now shows the new Holiday Inn look, very fresh and clean. Not all hallways are done, but rooms looked nice.
At times it gets crowded at reception with flight crews arriving or leaving. The breakfast is buffet style and very good. Prices can vary very much and when there is show/fair time in hanover it is very expensive.
A 2 min car drive from Hotel to airport terminal. Wifi worked.

Well, "Four Star Luxury" as declared at hotel door, in my opinion, is a bit exhagerated for this hotel, but pirce/quality ration is ok. The accomodation is a bit basic and (as usual in some German Hotel, especially near point of interest like an airport), the room price is ok, but breakfast and parking are very pricey. And I don't like the Holiday Inn use to give a poor basic "courtesy kit" in the bathroom with the necessity to ask for other thing at reception.
Overall, It is a good choice when someone have to arrive or depart from Hannover Hotel.

Telephone did not work.
Lack of coffee/tea making facilites - one tea bag, one coffee.
Free mimi bar contained one beer!
Nice clean room but very poor facilites.
Food mediocre, bland.
Will not be staying again.