That depends on the time frame you are asking about.

In the five years between 1970 and 1975 (the year the Khmer Rouge took over) the country was embroiled in a civil war between government forces led by Lon Nol and Sirak Matak against the communist armies of the Khmer Rouge and the North Vietnamese / NLF.

This period, known as the 'Khmer Republic', (the government formed by the men who staged a bloodless coup against the monarch Prince Sihanouk) is characterised by heavy amounts of corruption and the mental and physical stress of a population being bombarded by American planes as well as the wars of factions of communist guerillas. That being said, life still went on both in the country side and in the cities, the largest of which, Phnom Penh still functioned like any south east asian city. That is until it was besieged by the communists in 1974. It should be noted that the Khmer Rouge held vast areas of territory in Cambodia before their 'final victory' in 1975.

If the time frame you would like to know about is wider than that then it would make sense to differentiate Cambodia from both Thailand and Vietnam in a couple of important ways.

First of all, both Thailand and Vietnam are the hereditary enemies of the Khmer (Cambodians). Cambodia's forebear - the Khmer Empire (famous for its temples at Angkor) had a massive territory at its peak in the 12th century - covering most of mainland south east asia. Following a lengthy period of decline both the Thai kingdoms and the Dai Viet (Vietnamese) became much more powerful than the Khmer and Cambodia's borders shrunk to roughly where they are today. Notably, at various point both the territory surrounding Angkor (Siem Reap province and Battambang) were at times annexed by Thailand and in the south west of the country the area known as 'Kampuchea Krom' was annexed by the Vietnamese (it is still Vietnamese territory).

Cambodians always had an anxiety that one or both of these kingdoms would eventually swallow up Cambodia. A country with a large amount of land, but not a very large population.

Differences between the cultures of Thailand, Cambodia and Vietnam are numerous. For starters they all speak different languages, and have different religious cultures. Thailand and Cambodia are both Theravada Buddhist - but Cambodia converted to this faith in around the 13th century. Vietnam is more influenced by China than India, and ideas of Confucianism are mixed with Mahayana Buddhism rather than the more austere Theravada school. They all have indigenous customs and religious beliefs which co-exist with these larger religious systems.

To get to the main thrust of your question however, most of the countries in south east asia are highly influenced by what some scholars call 'monsoon culture', whereby the relationship between the land, the rain and agriculture figures heavily in society.

Walking through different towns or cities would not look drastically different between the three countries, and life would tend to revolve around similar things and practices.

To bring the discussion into more modern times (but before the wars in Indochina beginning soon after WWII) it would make sense to look at the influence that the colonial power of France had in the region. Vietnam, Laos and Cambodia were all French assets and Vietnam was the country treated with the most 'respect', if that word can be applied. What I mean by that is that the French used Vietnamese workers and administrators in taking care of important tasks in Cambodia, because they viewed the Khmer as lazy and incompetent. Therefore Phnom Penh, Cambodia's capital city, was heavily influenced by the whims of the French - but also maintained a large proportion of skilled Vietnamese people in it's population - for example of the one hundred thousand who lived in the capital in the 30's less than a third where Cambodian.

Life in the city was cosmopolitan, modern - Phnom Penh was known as the 'pearl of south east asia', until the wars began that is. The large central market was one of the biggest in the region, there were many chinese merchants, the royals maintained largely figure head roles but were visible to the populace. It was as Philip Short (author of an excellent biography of Pol Pot) called 'a strangely un-khmer city'.

In the country side it was a different story - very focused on the land and farming. Tight little villages that had little contact with the outside world and the cities - life revolved around the monsoon cycle and perhaps there would be a little shop that sold some wares imported from the city. Naturally advances in regard to transportation allowed a higher degree of mobility to some of the people in the country side but it was slight.

I am no expert in Thai and Vietnamese history but I know that in relation to Vietnam the Cambodian populace was left further behind than what the French had done in Vietnam. For example in 1930s out of about half a million school age children less than a few thousand had access to even the rudiments of a 'modern' education.

This is getting rather long so I will summarize for you:

It depends on where you are talking about in relation to 'pre-revolutionary' Cambodia. The city was cosmopolitan, mordern - rock and roll and bars and everything. Phnom Penh was a great city, not unlike others in SE Asia. (which is why it was such a big deal to march its 2 million inhabitants into the country side, dubbed 'new people')

The country side pre Khmer Rouge was characterised by a rural agrarian lifestyle, little education, lots of living off of the land and a focus on a spiritual co-existence with the land. (Why these people were designated the 'old people' in Democratic Kampuchea)

In regards to differences between Thailand and Vietnam, again it would depend on what kind of community you are asking about. I imagine rural communities wouldn't be that different (except for the cultural aspects) and the life in major cities wouldn't have been drastically different either (with Phnom Penh boasting a large population of Thai, Vietnamese and Chinese as well)

I hope that began to answer your question... I could recommend several books or documentaries if you would like to know more, I also started a podcast explaining the Khmer Rouge period that you can find at www.shadowsofutopia.com

Relevant Sources: P. Short 'Pol Pot: History of a Nightmare', D. Chandler 'A History of Cambodia', P. Yathay 'Stay Alive My Son'

I highly recommend the following books:

First They Killed My Father: A Daughter of Cambodia Remembers written by Loung Ung published 2000.

When Broken Glass Floats: Growing Up Under the Khmer Rouge written by Chanrithy Him published 2000.

Both of these books are written by childhood survivors of the Khmer Rouge and the “Killing Fields”. The stories cover their lives before, during and after.

The first chapters of Dr. Haing Ngor’s ‘Survival in the Killing Fields’ describes life before and during the rise of the Khmer Rouge. He also describes the relationship between Cambodia and its neighbours several times throughout. I highly recommend this book for an individual perspective on the genocide and how it came to be.