In my native language, there is a single word to express the high energy and enthusiasm shown by many at the beginning of a new job/project/romance etc. Normally it is used with a bit of skepticism/sarcasm.
I am looking for a single word or phrase in English that expresses the same
Honeymoon period is often used to refer to this time.
any new relationship characterized by an initial period of harmony and goodwill.
Novelty is related, particularly on the "used with a bit of scepticism" point. It typically indicates, if not enthusiasm, some level of interest found in a new and different situation.
"My new job is amazing!"
"Let's see if you still think that when the novelty's worn off."
Limerance: The magic of chemistry that happens in our brains when we fall in love.
Limerence has also been defined in terms of the potentially inspirational effects and the relationship to attachment theory, which is not exclusively sexual, as being "an involuntary potentially inspiring state of adoration and attachment to a limerent object involving intrusive and obsessive thoughts, feelings and behaviors from euphoria to despair, contingent on perceived emotional reciprocation”. -Wikepedia
Honeymoon period and infatuation are the two terms that spring to my mind.
The initial rush, though often used of drug induced euphoria or an adrenaline surge, can also be used to indicate the high of a new job or romance:
There's no way to fully recreate that new job feeling, but leaders can promote the ingredient that fuels the rush of a new job...
The rush of making a new friend can most definitely be likened to the rush of a new romance, things just feel a tad more exciting
In French there is a single word too, and I can find the following translations which are quite close to the idea you wish to convey:
Infatuation.
Google infatuation definition says:
an intense but short-lived passion or admiration for someone or something. "he had developed an infatuation with the girl"
Euphoria is one word used to describe that intense feeling of happiness and expectation.
A feeling or state of intense excitement and happiness:
in his euphoria, he had become convinced he could defeat them
The phrases love at first sight and at first blush both convey an initial infatuation that often is tempered by time.
The word gaga is about as positive as you can get and sums up your question.
not thinking clearly because you have very strong feelings of love for someone or because you are very enthusiastic or excited about something
Usage:
I had a great first date with Dan last night. I think I am gaga over him.New boss went gaga over my first few projects, now she expects perfect every time.
Consider the expressions:
"Things always look rosy at the beginning"
"The future always starts out looking rosy"
"Just wait until novelty wears off"
"New brooms sweep clean"
"Everything new is fine"
The word "zeal," or "zealousness," often indicates high energy or enthusiasm exerted towards a given activity. While it can be used in positive contexts, it also can be used cynically, as a way to to suggest that someone is too enthusiastic but lacks the experience that would give them a more balanced or laid back outlook.
smitten, this is probably what your looking for.
Rejuvenation
"to make (someone) feel or look young, healthy, or energetic again"
"Enchant" seems to work in: "John was enchanted by the possibility of being able to redeem himself."
Also, http://www.merriam-webster.com/dictionary/enchant gives us: "to attract and hold the attention of (someone) by being interesting, pretty, etc.", while Google gives us, as the first hit for "enchant", "fill (someone) with great delight; charm."
