We actually stayed for 4 nights over New Year's, and we couldn't have been more pleased. First off, though, you should be aware that this is not a classic "guest house": it's a hotel by every definition. We read many so-so reviews and decided to give it a chance anyway. We're happy we did.
The staff was friendly and helpful, the rooms were very clean, and the food at the restaurant was very good. The best thing: It's located on a very nice and relatively quiet street that's walking distance to Khaosan Rd, great food, and even the Grand Palace and Wat Pho (maybe 20 minutes). And, as the name suggests, it's right on the river (between two boat piers, actually).
One thing though- unless you REALLY want a room with a view of the river, don't pay the much higher price and instead opt for a standard - the rooms themselves are close to identical. There is no WiFi, but there is fast (and cheap) pay-as-you-go Internet in the lobby, and the front desk staff has loads of great info (and maps!).
Fantastic value for a midrange hotel!

Not easy to find and choose ONE hotel in BKK. New Siam fit the bill as I was looking for:
-Good location so I could myself locate the hotel anytime at night.
-Clean, safe, quiet, nice room, good value and close to Khao San without being right in it.

Im glad we made it in New Siam as I have no complaints whatsoever plus:
-Breakfast was gorgeous, very nice food in the terrace by the river.
-To be able to acces the Imperial palace, Wat Pho and other touristic sides by "riverbus" (pier is 2 min from hotel) is a trully fantastic experience
-Swimming pool turned out to be the most useful thing in the world after the first day in BKK

I did an enormous amount of research before I booked my first night in BKK and this place really worked for me. I would come back no doubt and would likely recommend to any friend

The rooms were slightly on the small size but good, with a nice view of the river (the river view rooms are the definate go). Our booking included breakfast, which is buffet style and good.
The outdoor area overlooking the river is quiet, pleasant and scenic.
Even though we had paid in advance the hotel asked for a refundable 1,000 baht "key deposit". No problems getting this back when we left, but it did tie up baht, which should be planned for.

The service was okay, but we felt that the hotel tried to charge for any extra, including some that might be considered basics. No wi-fi, and the lobby computers where a tad expensive (especially the printing).

Just across the road, and down an alley (the quickest way is the alley to the right of New Siam 2) is Khao Sam, which is a touristy narrow street with heaps of restaurants, bars etc.. From our perspective this was best in the daytime when it was not too crowded, and became a litle tiresome at night.

What is great value is the ferry that runs from the riverfront, which you can access from a walkway at the back of the hotel (turn right).the cost was 15 baht each way to the city. We didn't bother with the much more expensive cruise.

If you come to Bangkok you just have to visit Khao Sarn. It’s a back packer ghetto but in its dirty, scary, sleazy, and rip-off-the-tourist way, it is one of those things you just have to do. So staying here can be a fun experience, and also a necessity as Khao sarn is most fun at night.
Staying in Khao Sarn itself can be scary with all the druggies around (despite a police station near by). So we preffered to stay at new siam. Firstly make sure you get the the river view room that comes with a balcony. The rooms are nice and have the basics, although I had to tell the staff to get the toilet cleaned on the third day. Now wake up early morning to just see the river a little quite and then as it gets busier as time goes by. You can see the fantastic transition of bkk city as it wakes up.
The breakfast at this place is great too. Good food, and if you can manage to get a riverside table, that will be great too. Make sure you try the yummy pad thai. And try to avoid the pad thai at Khao sarn, cuz its atleast a few days old and can get you sick easily. The walk to khao sarn is very nice….but on the way back can get a little scary at night, especially if you’re alone. Just catch a taxi on the way back, only about 40bt.
Khao sarn is a one night visit, maybe 2 at the max. New siam is a safe and ideal place to stay