I attended a wedding there in 2016. I was in the bridal party.  

The wedding overall was nice and beautiful. If you want a mansion vibe and cannot afford or don't want Oheka Castle ... Bourne Mansion or DeSeversky are your next best bet.

let's start with the pro's....

-beautiful setting and curb side appeal. waterviews of the great south bay

-convenient location for guests (close to LIRR if you have guests from NYC)

-nice display of cocktail hour and viennese hour if you choose to upgrade that

- staff etc was great 

- ballroom was pretty (but oddly shaped-long room...dance floor all the way up front)

Now the cons.. unfortunately outweigh the pros in my opinion

Food was mediocre at best and I would honestly say some things especially my entree were inedible. Listen, it's a Lessings Caterer- anyone who tells you the food is amazing obviously does not really fancy or know quality food or been to an array of LI weddings. Look up reviews and research online- Lessing's has never proven to be exceptional in food. Call it a "chain" caterer- they have several venues across Long Island- the food must be mass produced and I do not believe some of the food I ate was made on the Bourne Mansion premises... 

I also felt like the mansion in general was a little rundown.. it had sort of a musty smell, the carpets in the rooms looked dingy. You can conceal all that with lighting and the ambiance you create- it is probably not a deal breaker. to me the food would be the deal breaker. 

just an FYI- rumor has it they are supposedly closing and were recently bought. I would highly recommend you ask questions about this if you are booking into late 2018/early 2019.