Still in school but no longer a student
Academic work is done usually at the university. However, you will become an employee, and no longer have student rights, such as the cheapest food at the cafeteria. You will still get a staff discount though, so it’s not too bad. Additionally, if you feel like still socializing at a student level, you will find it very difficult as your PhD will be literally a job, with work times, salary, holidays, etc. Some of your peers might still be frequenting social events, while you may not be able to due to your having to be in the office the next day in the morning.
More money but less money
In Finland, PhD salaries are very fair. However, they can be on average below the salaries offered by private companies. Nevertheless, coming from a student allowance to an actual salary (or grant) is a great upgrade. And speaking of grants, there is a caveat that if there is no salary budgeted for your position, you might have to rely on applying to numerous grants to sustain your work and livelihood. And in general, personal grants are usually not as large as salaries.
Flexible time and overtime
Normally, you will have a large amount of control on how many hours you spend at the office or laboratory and how many hours you spend outside of it. Of course you will have to agree with your Professor on that matter. Some research units like that their researchers do the classic 9-to-5 work, while others allow you to work flexibly as long as you get your results on time. This is a big advantage, as it allows you to balance your work life and personal life effectively. However, this can also lead to long work days and even work weekends, which will of course does not translate to extra pay. The author does not recommend taking work home or working on weekends.
A thankless gratifying endeavour
In the past they said that “great science is built on the shoulders of giants”. Nowadays, research appears to be built on the shoulders of thousands of tiny giants. And your scientific contribution might feel like a speck of dust in a universe of publications. Unless you happen to do some groundbreaking work that is published in a famous international journal, you may feel that your work is unappreciated. However, not only is your work one of those giants on which future researchers will stand, but also there are few things as gratifying as receiving that email that your paper was accepted for publication.
A great job in the future that will be hard to get
Getting a job after graduation is hard for everyone. However, for a PhD graduate, it might be even harder. There are two choices for a PhD graduate: a tenure track career path in Academia or a company job. Both have their pros and cons and their challenges. A tenure track is a pathway to a permanent position at a university, while a company job is self explanatory. Being granted a tenure track position can be very challenging due to the very few positions usually available and the high competition. Additionally, you might need to do a 2-year postdoc before you are even eligible for it. If you decide to go for a company job, you will find yourself with the similar issues regarding offer and competition. Your knowledge at this point will be very specialized so it might be difficult to find a position in a company that fits your expertise. But once you land either a tenure track position or a company job, you will be filled with great satisfaction and new challenges.
Naturally everyone’s experience will be different. Some people will have an easy time and some will have a very hard time. Most will have a combination of ups and downs. However, if you feel lost, you should always have a conversation with your PhD supervisor or advisor, and they will certainly guide you in the right direction.
Edited 26.9.2019 22.15: Clarified wording on tenure track career path and tenure track positions.