Upsides:
+ Your reports will treat you with respect
+ You will get more opportunities to travel
+ You will likely get much more visibility in the organization
+ You will get the opportunity to engage in team building activities and have fun
+ You can set the standards and direction of the group
Downsides:
- You will have to learn the art of politics to deal with your peers
- You need to be much more cautious about your communication and actions
- You have a target on your back and so you need to learn how to block
- You will likely have to spend more money on corporate travel & activities than your used to
- You have to have the maturity to deal with 'wasteful' activities that are part of management
One of the biggest problems with people being asked to be a manager is whether or not the organization is asking for a real "manager" or a "leader". This is a particular problem with technical staff being promoted to management.
Managers by definition are there to set everyone straight. Define the rules. Make the process repeatable. Make sure no one is out of line.
However, many companies are not really seeking this from technical staff. What they really want are "leaders". If people are asking you as a manager to set the technical direction or lead and train the engineers or give presentations at conferences, they're not asking for a traditional "manager". Ultimately, if you seek to be a traditional manager (in this type of environment) you're doomed to fail.
Great people managers are really a type of coach. They give pep talks, they throw events, they motivate, recruit the best talent, etc. Think of your high school football coach.
In this style of management you're going to be graded on retention, motivation, drive, energy, etc. etc. If this isn't you, you better think twice about moving from engineering.
If this organization is really looking for an Architect or Principal Engineer that will dive the direction and strategy for their technology, they let them know that.