I've run the gamut of hotels in Bangkok. From the economic choices to the high-end properties. I would consider the Peninsula Bangkok the best overall value worldwide.
There are other reviews that will tell you about the luxurious amenities and the speedy and efficient check-in.
I want to talk about the other options one has when traveling in Bangkok. We're talking about staying in one of the finest hotels in the world, for around $250 a night.
True this hotel is on the river, away from all the hullabaloo of Sukhumvit. The ferry and the skytrain make the trip fairly painless.
All this culminates in me not staying anywhere else while I'm in Bangkok.

We spent 4 glorious nights/days at the Peninsula. What a wonderful hotel! The staff, the food, the rooms, the restaurants, the swimming pool, everything is top of the line.
The views of the river from our room were spectacular and the gardens on the property amazing. It was great to sit at the river cafe for breakfast and evening drinks. The swimming pool was gorgeous! It even had "salas' for two. Towels & cold water were provided as soon as you sat at the chaise loungers. A tasty trail mix was served with drinks. Apples were available as well.
Breakfast was excellent, with many, many choices, both Asian & Western.
Dinner at the River Cafe & Terrace was a scrumptuous event. High quality meats, and seafood, including beef & lamb, large prawns,scallops, tuna, etc were grilled to order. There were sushi, curries, salads, rice, pasta, breads, cheeses, and delicious deserts of all kinds. Amazing and worth the money.
The staff everywhere was very serviceable and always smiling.
Their river boats are beautiful, very convenient, and efficient.
This is a world class hotel which made our stay in Bangkok even more perfect!

On arrival we were upgraded from G D/L room to a G D/L suite. This was a very impressive space with an exceptional view of the river and sky line on the opposite side. The service was impressive. The pool amenities top notch as was the food on the riverside patio. If I can find a negative, it is the lack of sit down space inside the front door as this is used to serve breakfast and afternoon tea. This must rank as one of the best hotels anywhere.

During 2008 business and leisure persuits have called me to Bangkok for three months. I've made the Peninsula my home for these three month of 2008 and it has been an incredible experience.

Service:

From the valet boys at the front door, bellmen, concierge, etc all I can say is "wow". Superbly efficient and genuinely concerned for their guests satisfaction. The Peninsula staff are very well trained and take guest service very seriously. Service requests are excecuted quickly and efficiently with a warm Thai smile.

The staff of the Peninsula Bangkok are world class and will attend to anything you may need.

Rooms:

The Peninsula Bangkok is celebrating it's 10th anniversary this year and I must say rooms are very well maintained and "fresh". Housekeeping is impeccable. All rooms offer sweeping views over the river to the city skyline. It is one of the greatest urban skyline views and it's at your window when you have the pleasure of staying in the Peninsula.

Suites are well worth the splurge offering a seperate living room with a small dining table, comfortable sofa and 2 side chairs. Additionally an adequate sized desk for work station is provided. Decor is restrained in a classical luxury hotel manner with wainscotted walls, oatmeal colored wool carpeting, harwood floor entryways and lavish marble ensuite bathrooms.

Rooms overall are very well designed and supremely comfortable even for a long term stay. Please note that they are lacking flat screen televisions and sound systems urgently need updating. Additionally in room internet (while free) can be erratic and very slow at times.

Pool, Spa & Gym:

Fabulous - a resort feel in a city hotel. The pool is stunning right on the Chao Praya River. The long pool with Thai Salas is a true oasis in the heart of the city with fantastic waiters offering top quality poolside food and beverage. A great place to relax and pass the day.

The Spa is gorgeous with sumptious treatment rooms and highly skilled therapists. Well worth doing!

The gym while a bit small is rarely crowded and adequate for a good work out. Personal trainers are always on standy by in the gym.

Dining Venues:

Thiptara, the Peninsula's signature Thai restaurant is not to be missed. Stunning garden setting right on the Chao Praya river. Delicious food served by a delightful and professional staff.

Afternoon Tea in the Lobby Lounge is a scrumptious must do experience. Don't miss it!

Most other meals I enjoy via room service which is always prompt and professional. The food quality is good and special requests are happily catered to.

Overall I can't stress enough how exceptionally comfortable, warm and inviting this world renowned hotel is. The Thai staff really make it feel like home. I can't imagine staying anywhere else in Bangkok. Highly recommended!