The Lufthansa Business and Senator lounge in Hannover (HAJ) is located in terminal A. This is a typical Lufthansa lounge and have you ever visited other Lufthansa lounges you will more or less know what to expect. I went to the Senator lounge that is not particular large, but there was plenty of space during my visit. My guess is it could be crowded at times. The lounge is divided into a few different sections including a table/dining area and an area with resting chair. The interior is in a good condition and the lounge looks relative newly remodelled.
Generally I am very pleased with the Senators lounges, mainly because some sort of warm food is always available, and they have a decent selection of drinks including soft drinks, coffee, tea, wine, and a selection of German beer. Especially in comparison to other Star Alliance lounges in Europe and the US the food options are better. My only appeal is that they more or less serve the same food in all the lounges and some variation could be nice.
In conclusion the Lufthansa Senator lounge in Hannover is decent. The place was not crowded during my visit, the lounge is a in a good condition, and the food options are good. Great place for a break before a flight.