I can only see 1 review rated at 2 stars and somehow TripAdvisor is showing 4 stars!!! Very similar experience. Was on the road from Medan via Berastagi and Ketambe and on to Banda. A bad fall in Ketambe meant I had six stiches so was really looking forward to staying here after 8 hours of winding roads in a minibus. The deal was that Renggali is the best place to stay in Takengon. Got there after dark and there was nothing much to write about... except for some of thw worst experiences of staying in a hotel.
First up, at about 250000 rupiah (rack rate 350K upwards), this is as expensive as it gets in the region and Takengon is a small town at best. No one spoke English, which is alright; I love it when we don't know languages... it's fun. But that was it.
The entire hotel was empty but they refused to give me a lower rate or accommodate in the reception building even though I had a really bad leg. With no option, I finally went to the standard rooms quite far (corridors open out to the lake). The first room was stinking, old, lights were too low to read a book, bathroom was dirty... you get the idea. So I had to send them off to get some more keys.
Four rooms later, I selected one that didn't stink as much and felt relatively clear. Must have spent an hour trying to do this. Asked for clean towels, toilet paper, blankets, ... phew!
Midway through, the lights went out. So, well, no hot water or any water, for that matter, since the pump won't run.
That's not it. They don't have a kitchen for lunch or dinner. Your only option is to get a becak and ride to town. The becak costs 40,000 rupiah (20000 if you can haggle well). So, really, the cost for a room here is more like 400,000. Breakfast is served though ;-D
In the morning, just when I was about to brush, the electricity went out. It didn't come back till my minibus arrived, so no bath at all. Luckily, they had a water dispenser. So much for being the best hotel in Takengon.
Fortunately, I had not paid in full so I refused to pay, wrote a big complaint letter and left.
The view is amazing though ;-D
My two cents... stay in town. Any of the hotels in the regions are infinitely better even at a fraction of the price. You can come over to the lake in a becak or walk over from town.

I spent one night at Hotel Renggali, which is in the Gayo Highlands of Nothern Sumatra, next to Lake Laut Tawar. After a 10-hour drive from Medan, the first thing I wanted to do was use the bathroom. There was no toilet paper. The staff rolled their eyes when I asked for some, like I was being high maintenance or something. After that, the toilet wouldn't flush, so I had to get one of the staff to come to my room. He treated me like I was stupid for not realizing that their malfunctioning toilet has to be flushed not only by the handle, but also by turning the water supply on and off from underneath.

It was cold in the mountains, probably in the 50s at night, but there was no heating, and the bed only had two thin sheets on it, no blanket or comforter. Once again, the hotel staff treated me like I was asking way too much from them when I asked for a blanket. The hotel looks like it was built in the 1970s and hasn't ever been renovated or cleaned. Everything was dusty, the TV didn't work, and worst of all, the bed was covered in dead mosquitoes. I tried brushing them off, but most of them just smeared all over the sheets. The blanket was really thin, so I shivered the whole night on a bed of smeared mosquitoes.

In the morning, I was amazed. The back of the room has windows that open up to a veranda with a gorgeous view of the lake. It was absolutely breathtaking to watch the sun rise over the lake and mountains. With that having been said, I'm told that this is the nicest hotel in the area, so I don't recommend that anyone ever go out of their way for this trip. There are other lakes in mountains in Sumatra that are near better hotels and are warm enough for swimming. Avoid this hotel if possible.