I do both and I feel your pain

! Most people I saw trying the swing ER/ICU didn't like it. either they had to much ER or ICU blood in there veins!! But I am 3/4 ER and 1/4 ICU( it most be from my mom 8). It is different. I work in one of the most busy critical care hospital in Canada. Our acuity is very high cause we cover alot of geography. First the thinking. The patient aproach is veryy different. An ER RN have to know a little bit about alot and an ICU alot about a little bit. We aproach with symtoms they aproach by system. Personally, I believe ICU nurse know more there pathophysiology in depth then we do. That's one of the reason I like to go back. Ask an emergency nurse to define you shock and they will tell you about BP , sign and symtoms and heart rate. The icu nurse, they will start explaining you the afterload CVP, pressure wedge, SVO2 and the reason why you have an increase blood sugar. So first you be a very curious and ready for such mental challenge.
I know you guys do things different they us. But here what a day kind look like. Assessment head to toe. When I say head to toe I really mean it!8) We kind do a generalise assesment according to the complaint, they go in very details. Usually because they have 1 patient, so much more time. But one mistake ER RN do, when it come to patient load. They believe since they can take care of 3-6 at the same time, it will be easy to just have one.They have more things going on and require alot of nursing care. Therefore the reason why they are one on one. After you assesment, charting ( we do it on computer) Then you get ready for rounds. Where you have to give your opinion in front of 12 people. So you ahve to be prepare. That mean you have to read the chart, review medication list, ect. Then start the CT here, X-ray there. If your lucky, you have a "stable" one and those are the one the ER people don't really like. Cause there alot of waiting. But That give you more time to interact with family, read more on the condition of your patient or chat with staff.
I really like the interaction with family. you get to know them and find to make a better impact. when they come in the ER, they are still under shock and are not really sure what's going on. I still remember that men who I took care of his son. I cleaned the blood off is face. Simple gesture, right? Well almost 2 years later in a middle of a conference with close to 100 people in the room. He notice me and thank me again. Other good stuff in the ICU, the gadget. yes I know, a guy thing. We get to play with numbers and monitoring which help you prevent the patient to decompensate. Most of the patient also, don't rename ,in a name your mom woudn't be proud cause they are drunk. most of them are pretty quiet. You also get to play with drip and all.
In all if you have a chance to do both. Go ahead. I work in the ICU causal and it make me a better nurse in both field with the experience that i bring from one to the other. But if you have to make the full jump, maybe do some shadow shift with a nurse at your center. Cause you are always more one then the other. Hope I help