As an American we always here about the tenaciousness of the Japanese, the machine-like precision of the Germans, or even the remorselessness of the Red Army. What we hear about is how these armies viewed or now view the US or even UK troops. We are always told about the plucky never say die attitude, but it would be interesting to hear from the other side for a change.
This of course very subjective, but in general:
The British were considered masters of naval warfare (more or less naturally), especially offensive naval warfare, to the extent that they designed the Nelson class to have most of its guns forward-facing, since the Royal navy would always be trying to close with the enemy rather than the other way around. The British army was considered small but high-quality. The British excelled at logistics and at defence - Hitler himself said that once an Englishman had sat hiumself down, there was no removing him. The British were also known for their patrolling activities, attempting to dominate the terrain between the lines of themselves and their enemy, many of which were conducted at night. The Germans noted the British problems with integrating different arms during the early part of ww2 - not using AT guns and tanks in unison, tanks charging ahead without infantry, artillery and AT support. In general, the British were considered non-quitters. They kept fighting, they kept trying and they continued until they found a solution.
The Canadians had a reputation from ww1 for being among the best of the allied troops - early adoptors of combined arms, competent officers chosen by merit rather than connections or blood. They fought alongside the British with the same uniforms, weapons, organisation and doctrine and generally had the same attitude as them.
The Australians were from the start all volunteers and the recruites could have their pick of the best men - the Germans noted that the Australians fighting at Tobruk 1941 all seemed to be tall, strong men. These men had the same initiative as the British, fighting along the same doctrine and with pretty much the same weapon, but seemed to have a lack of formality and class stratification, which created very strong unit cohesion that endured extreme hardships.
The Indians were viewed with mixed opintions. Some of the Indian units were pre-war professional units and fought extremely well, such as the 4. Indian Division, while others lacked in training and unit cohesion and were quickly over-run. Each Indian division included a Ghurka battalion, and these men were universally feared. It is said that the Japanese feared no allied soldier in melee - except the Ghurkas. A German joke from the Italian front (where the 4. Indian Division fought) was;
How do you know you have been decapitated by a Ghurka?
You dont, until you sneeze.
The Americans were feared for their firepower - especially their artillery (which had an insanely superb system to quickly get fire on the right spot), but their infantry was viewed as less potent on their own than German infantry - the lack of a true LMG in the US army (since the BAR did not have an interchangable barrel and was thus incapable of sustained fire) reduced the ability of the US infantry to pin their enemies - generally the Americans were considered "soft" - ie they would balk at casualties, but their artillery was rightfully feared and their logistics and industrial ability to arm and supply their troops were universally respected. I have heard second-hand account from a German veteran (his nephew told me) that "We knew the war was lost when we found high-quality American meat tins in knocked out Soviet tanks."